High Pitch Sound From Diff

Hey guys, had my car for about 3 months and started to notice a weird sound that's in the way of enjoying my dream car. Really appreciate your help on this. E92 M3 2008, 100% stock, no mods, 6 MT, 65K miles.

There's a soft, high-pitch whine coming from the engine bay, near the drivers side. I uploaded a video on YT. Ignore the squeaks in the video, that's the rear suspension. My main concern is the high pitch noise most apparent in beginning of video:
The car only makes this noise when:

-Engine has warmed past 175 F
-In 4th, 5th, or 6th gear (most notable in 6th)
-Between 2500-3000 RPM (most notable in 3000)
-Foot is on throttle (stops immediately once I let off)

A/C on or off makes no difference. Inspected all air filters but looked fine, considering replacing them but wanted to know if anyone experienced this??

joyjoy22 wrote

You should probably check your engine belt as it one of the primary reasons why you hear a high pitched while driving.

thanks il try that. dam another maintenance...thing's a money pit

Update: belts look fine. I've been reading into "normal" sounds from the engine according to this thread. It seems this person claims there's intake resonance depending on the air filter. Was curious if anyone else experiences this at around 3-4K RPM? I'm running the OE Mahle filter

I can barely hear it. How loud is it relative to the rest of the sounds you hear when driving? Check the power steering fluid level? The pump will whine when it's running low on fluid. Other than that, check all your intake and plenum fittings to make sure theres nothing loose, make sure the air filter is seated correctly since it's annoying to pop in, check all pulleys and tensioners to make sure they're not wobbly.

I don't know what else I don't think I've heard that exact whine

RedScytheM3 wrote

I can barely hear it. How loud is it relative to the rest of the sounds you hear when driving? Check the power steering fluid level? The pump will whine when it's running low on fluid. Other than that, check all your intake and plenum fittings to make sure theres nothing loose, make sure the air filter is seated correctly since it's annoying to pop in, check all pulleys and tensioners to make sure they're not wobbly.

I don't know what else I don't think I've heard that exact whine

it's loud enough to bother me, kind of like hearing a whistle from far away. Power steering fluid level is fine, no issue with turning the wheel. I had checked the plenum and airbox for gaps but looked okay. I can't get to the tensioner or pulley easily, but I'll try this week.

My guess it's some atmospheric pressure noise when the intake valve is closed; The fact that it only appears around 3K in higher gears makes me suspicious of this. I also read that the plenum cover can have some gaps in the gasket, so I'll check that out this week as well

it's this... go to post 28

https://www.m3post.com/forums/showthread.php?t=1417824&page=2

Fooksdaddy wrote

it's this... go to post 28

https://www.m3post.com/forums/showthread.php?t=1417824&page=2

Thanks, I read this thread before but the person said the sympton occurred when the car is stationary. However now I see that another person reported the same symptoms as mine when the car is in 4-7 gears. Will try this!

MattyRice wrote

Fooksdaddy wrote

it's this... go to post 28

https://www.m3post.com/forums/showthread.php?t=1417824&page=2

Thanks, I read this thread before but the person said the sympton occurred when the car is stationary. However now I see that another person reported the same symptoms as mine when the car is in 4-7 gears. Will try this!

super easy to not give it a look.... hopefully fixes it.

Fooksdaddy wrote

super easy to not give it a look.... hopefully fixes it.

Wow finally got the plenum open, and I was surprised to see idle air nozzle is different than my expectations, BMW must have put different plenums on 2008s. Here's what I expected (circled in red) vs what mine looks like. Since I already had the plenum out I decided to follow that thread and use RTV silicone gasket maker. Didnt feel any gap unfortunately, so going to test drive it this weekend if it works. If it doesn't work, I'll remove the air filter to see if that's what's causing the noise too

What i expected:


Mine:

update: there's still the faintest noise but it's now unnoticeable over music/windows down. Not sure if I put enough RTV or just buy a new air filter, or maybe even the plenum is more secure than prior. Either way I can live with this. thanks all!

MattyRice wrote

update: there's still the faintest noise but it's now unnoticeable over music/windows down. Not sure if I put enough RTV or just buy a new air filter, or maybe even the plenum is more secure than prior. Either way I can live with this. thanks all!

It's odd that you mention this. I too have recently heard a noise on my 2008 but after putting in a new K&N and replacing a couple of the screws to hold the cover on. I wonder if the noise is in the elbow up front. it was a pain to get on. I will recheck mine.

timtech wrote

MattyRice wrote

update: there's still the faintest noise but it's now unnoticeable over music/windows down. Not sure if I put enough RTV or just buy a new air filter, or maybe even the plenum is more secure than prior. Either way I can live with this. thanks all!

It's odd that you mention this. I too have recently heard a noise on my 2008 but after putting in a new K&N and replacing a couple of the screws to hold the cover on. I wonder if the noise is in the elbow up front. it was a pain to get on. I will recheck mine.

timtech wrote

MattyRice wrote

update: there's still the faintest noise but it's now unnoticeable over music/windows down. Not sure if I put enough RTV or just buy a new air filter, or maybe even the plenum is more secure than prior. Either way I can live with this. thanks all!

It's odd that you mention this. I too have recently heard a noise on my 2008 but after putting in a new K&N and replacing a couple of the screws to hold the cover on. I wonder if the noise is in the elbow up front. it was a pain to get on. I will recheck mine.

I just drove without my air filter (scary) and confirmed it's not the cause. not sure why the elbow would cause it either. I'm sure it's the plenum,maybe I didn't put enough RTV on it..

Problem still persists, asking the forum gods if there's any remedy to this...can't stand the noise. It's like a clarinet playing softly and now I'm ultra sensitive to it. Only happens after car has warmed, 3K rpm, and throttle is pressed. Starting to wonder if this is normal..

-Disconnected the ISV hose (rear right) from the plenum, no change
-Patched plenum ISV inlet rubber part with RTV as suggested, no change
-Removed air filter, no change
-Checked belts, no apparent damage
-Elbows and fittings are tight around intake
-Power steering fluid ok

Couldn't really hear it on my work computer but your issue sounds similar to what I was experiencing. I was getting a whistling/humming noise around 45-50mph & 65-70mph any gear, any rpm. I thought it might be the wheel bearings but the noise would disappear as soon as I clutched in. After doing more research it sounded like it might be coming from the diff. Supposedly it will make a humming sound once the ring and pinion(?) starts going bad.

Unfortunately I wasn't able to resolve it. I did replace the diff w/ a rebuilt one but I also upgraded my differential and subframe bushings so now I have even more whine than before. At least now I know it's suppose to whine lol. But yea, look into the diff, but it's hard to diagnose because you would have to replace it. Good luck.

STooK wrote

Couldn't really hear it on my work computer but your issue sounds similar to what I was experiencing. I was getting a whistling/humming noise around 45-50mph & 65-70mph any gear, any rpm. I thought it might be the wheel bearings but the noise would disappear as soon as I clutched in. After doing more research it sounded like it might be coming from the diff. Supposedly it will make a humming sound once the ring and pinion(?) starts going bad.

Unfortunately I wasn't able to resolve it. I did replace the diff w/ a rebuilt one but I also upgraded my differential and subframe bushings so now I have even more whine than before. At least now I know it's suppose to whine lol. But yea, look into the diff, but it's hard to diagnose because you would have to replace it. Good luck.

Appreciate the tip. I checked some videos and I came across this. It's really close but curious if your noise came from the rear? I can isolate mine from the front. If it was the diff, I would think the noise would be from the mid-rear and not the front?

STooK wrote

Couldn't really hear it on my work computer but your issue sounds similar to what I was experiencing. I was getting a whistling/humming noise around 45-50mph & 65-70mph any gear, any rpm. I thought it might be the wheel bearings but the noise would disappear as soon as I clutched in. After doing more research it sounded like it might be coming from the diff. Supposedly it will make a humming sound once the ring and pinion(?) starts going bad.

Unfortunately I wasn't able to resolve it. I did replace the diff w/ a rebuilt one but I also upgraded my differential and subframe bushings so now I have even more whine than before. At least now I know it's suppose to whine lol. But yea, look into the diff, but it's hard to diagnose because you would have to replace it. Good luck.

Dam I think you're right. Got a video from the rear and it's more pronounced in the video than what I took originally from the front. I'll take it in to check the fluid, but the prior owner changed it 15K miles ago

MattyRice wrote

Dam I think you're right. Got a video from the rear and it's more pronounced in the video than what I took originally from the front. I'll take it in to check the fluid, but the prior owner changed it 15K miles ago

Is this your video or someone else's? I was able to hear the noise in this one (starting around 25 seconds) and it's the EXACT same noise I had. I also couldn't tell if it was from the front or rear but leaned towards the rear because I could capture the sound better facing the rear. (Wouldn't even pick it up facing foward)

Mine would start around 60, 65, or 70mph and hum/whine when I was on the gas and slightly go away off the gas. It would also completely disappear once I pushed in my clutch. It's not a very loud hum but I know it definitely wasn't there before so it would bother me every time I drove it. Unfortunately, I couldn't find a solution to this issue.

I would start with a diff flush (mine came out black) but I think if you're hearing the noise already it's too late. I changed mine and the noise was still there. The issue must not be too common because I only found 1 other case and the owner sold the car before figuring it out. You probably don't need to change the diff anytime soon though, my mechanic said there wasn't much play in my diff when he removed it so I'm thinking you can drive on it for a while and see if it gets louder. Only bad part is you're gona have to live with it. Another option would be to order a new rebuilt diff from diffsonline.com and install that (or take a chance with a used diff).

Let me know if you find out what it is, maybe it will even turn out to be something else. Good luck and keep us posted.

STooK wrote

MattyRice wrote

Dam I think you're right. Got a video from the rear and it's more pronounced in the video than what I took originally from the front. I'll take it in to check the fluid, but the prior owner changed it 15K miles ago

Is this your video or someone else's? I was able to hear the noise in this one (starting around 25 seconds) and it's the EXACT same noise I had. I also couldn't tell if it was from the front or rear but leaned towards the rear because I could capture the sound better facing the rear. (Wouldn't even pick it up facing foward)

Mine would start around 60, 65, or 70mph and hum/whine when I was on the gas and slightly go away off the gas. It would also completely disappear once I pushed in my clutch. It's not a very loud hum but I know it definitely wasn't there before so it would bother me every time I drove it. Unfortunately, I couldn't find a solution to this issue.

I would start with a diff flush (mine came out black) but I think if you're hearing the noise already it's too late. I changed mine and the noise was still there. The issue must not be too common because I only found 1 other case and the owner sold the car before figuring it out. You probably don't need to change the diff anytime soon though, my mechanic said there wasn't much play in my diff when he removed it so I'm thinking you can drive on it for a while and see if it gets louder. Only bad part is you're gona have to live with it. Another option would be to order a new rebuilt diff from diffsonline.com and install that (or take a chance with a used diff).

Let me know if you find out what it is, maybe it will even turn out to be something else. Good luck and keep us posted.

appreciate it!! yes this is my video. God I'm super upset, there's always something going on with this car. il keep this updated, going into shop on monday

MattyRice wrote

STooK wrote

MattyRice wrote

Dam I think you're right. Got a video from the rear and it's more pronounced in the video than what I took originally from the front. I'll take it in to check the fluid, but the prior owner changed it 15K miles ago

Is this your video or someone else's? I was able to hear the noise in this one (starting around 25 seconds) and it's the EXACT same noise I had. I also couldn't tell if it was from the front or rear but leaned towards the rear because I could capture the sound better facing the rear. (Wouldn't even pick it up facing foward)

Mine would start around 60, 65, or 70mph and hum/whine when I was on the gas and slightly go away off the gas. It would also completely disappear once I pushed in my clutch. It's not a very loud hum but I know it definitely wasn't there before so it would bother me every time I drove it. Unfortunately, I couldn't find a solution to this issue.

I would start with a diff flush (mine came out black) but I think if you're hearing the noise already it's too late. I changed mine and the noise was still there. The issue must not be too common because I only found 1 other case and the owner sold the car before figuring it out. You probably don't need to change the diff anytime soon though, my mechanic said there wasn't much play in my diff when he removed it so I'm thinking you can drive on it for a while and see if it gets louder. Only bad part is you're gona have to live with it. Another option would be to order a new rebuilt diff from diffsonline.com and install that (or take a chance with a used diff).

Let me know if you find out what it is, maybe it will even turn out to be something else. Good luck and keep us posted.

appreciate it!! yes this is my video. God I'm super upset, there's always something going on with this car. il keep this updated, going into shop on monday

here's a whole thread I just found from 2008..basically affects some small number and they switch out the diff...gawd

https://www.m3post.com/forums/showthread.php?t=134153

MattyRice wrote

here's a whole thread I just found from 2008..basically affects some small number and they switch out the diff...gawd

https://www.m3post.com/forums/showthread.php?t=134153

I've read that thread before but I'm not sure if they're related. I always had a whine/hum at 45mph and I believed it was just a normal characteristic of the car. But my concern was it started humming again on highway speeds at 65-70mph and it wouldn't go away even if I went faster. At what speed do you hear yours?

STooK wrote

I've read that thread before but I'm not sure if they're related. I always had a whine/hum at 45mph and I believed it was just a normal characteristic of the car. But my concern was it started humming again on highway speeds at 65-70mph and it wouldn't go away even if I went faster. At what speed do you hear yours?

Same mine is about 45mph and again 60-70mph (2.5K-3K rpm each). But it does go away once I pass those bands, or the sound drones out next to the V8 since that's higher RPM. I've noticed 4th and 6th gear are most pronounced, which suggests a certain load on the engine is required before I hear the noise. It also goes away once I remove throttle, which leads me to suspect the pinion gear is related (it moves upon throttle). This is similar to that thread. Also someone on that thread replaced their diff, and the sound went away, indicating it's not normal. In my video it's loud enough where it's bothersome, so I would expect more posts on this. Also my car is 08 with 65K miles. I read the service life is 80K (which is absurd), but there you have it; BMW mastercrafting the engine only to fall asleep at the wheel.

I also found a few websites that gives more description. Bit of a hole-in-the-wall websites, but it lines up. Only question is what they refer to as "howling". Sounds are suggestive, hence me recording my own. They both suggest lubrication and/or gears as the problem. I'm saddened that the prior threads report different lube does not remedy this.


"Howling under acceleration at various speeds, however, indicates that the gears are already worn out or are out of alignment or depth with each other. If rear differential noise occurs while accelerating the car only at a certain speed, it is likely because the gears have become worn due to overloading and lubrication failure. If your gears are newly installed and still create a howling noise, double-check its preload and make sure that the teeth are properly aligned."

https://fuelandfriction.com/weekend-warrior/understanding-rear-differential-noise/


"Noise: Howling while accelerating over a small speed range (gears previously quiet)
Cause: Worn gear set due to lack of lubrication or overloading"

https://www.onallcylinders.com/2012/03/30/quick-guide-to-diagnosing-differential-driveline-noises/

MattyRice wrote

Same mine is about 45mph and again 60-70mph (2.5K-3K rpm each). But it does go away once I pass those bands, or the sound drones out next to the V8 since that's higher RPM. I've noticed 4th and 6th gear are most pronounced, which suggests a certain load on the engine is required before I hear the noise. It also goes away once I remove throttle, which leads me to suspect the pinion gear is related (it moves upon throttle). This is similar to that thread. Also someone on that thread replaced their diff, and the sound went away, indicating it's not normal. In my video it's loud enough where it's bothersome, so I would expect more posts on this. Also my car is 08 with 65K miles. I read the service life is 80K (which is absurd), but there you have it; BMW mastercrafting the engine only to fall asleep at the wheel.

I also found a few websites that gives more description. Bit of a hole-in-the-wall websites, but it lines up. Only question is what they refer to as "howling". Sounds are suggestive, hence me recording my own. They both suggest lubrication and/or gears as the problem. I'm saddened that the prior threads report different lube does not remedy this.


"Howling under acceleration at various speeds, however, indicates that the gears are already worn out or are out of alignment or depth with each other. If rear differential noise occurs while accelerating the car only at a certain speed, it is likely because the gears have become worn due to overloading and lubrication failure. If your gears are newly installed and still create a howling noise, double-check its preload and make sure that the teeth are properly aligned."

https://fuelandfriction.com/weekend-warrior/understanding-rear-differential-noise/


"Noise: Howling while accelerating over a small speed range (gears previously quiet)
Cause: Worn gear set due to lack of lubrication or overloading"

https://www.onallcylinders.com/2012/03/30/quick-guide-to-diagnosing-differential-driveline-noises/

Yup, sounds like we have the exact same issue. I also found it hard to believe that there aren't more people with the same issue out there.

So what are you going to do? Sounds like the only option is to replace the diff or rebuild it. Either way it's gona be costly...