New Engine Mounts Causing Interior Rattle

Hey All!

I just got my rod bearings done and naturally also had my engine mounts swapped out. My old ones were completely collapsed and I replaced them with the bimmerworld uprated mounts. I know that these mounts are firmer than the OEM ones, but I'm hearing this pretty obtrusive and abnormal sounding rattle/vibration/burbling on the passenger side of my car. It waxes and wanes as the car idles. The tach doesn't move, but you can hear the engine sort of shift it's idle a little bit, and the sound occurs when it's at the lower point of the idle. I haven't been able to narrow it down to any point in the interior or exterior, so I'd appreciate any pointers on where to look.

Thanks!

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Do you happen to know how your transmission mounts look? Pretty common for these to cause vibration in the cabin as well.

yardbro wrote

Do you happen to know how your transmission mounts look? Pretty common for these to cause vibration in the cabin as well.

I don't, but I will certainly investigate. And along these lines, I actually think I have a suspicion on what it could be. My car has test pipes (came with it when I bought it) and I suspect they might have sheered off one of the exhaust mounting points (common issue) and there might be a leak that's causing even more vibration. I'm planning on heading to an exhaust/muffler shop to have the test pipes welded vs. using the clamps and having them remove the bracket in question, linked right here: https://www.turnermotorsport.com/p-47859-18207841053-genuine-bmw-part/

And while you're down there, check all your heat shields - make sure they're not touching any metal parts, and that all the screws/clips are in place. Same for the underbody felt/plastic panels. My money says it's probably one of these as a broken exhaust bracket sounds more metallic.

How many miles have you put on the car since the mounts were installed?

I had my rod bearings done last summer, and also replaced my mounts with BW's. I was shocked at how much NVH was introduced when I first fired up the car, but it settled down after ~100mi of driving, and then it was basically back to stock.

From personal experience, BimmerWorld motor mounts will cause significant NVH during the initial couple hundred miles, especially when engine is cold! It gradually gets better by 1000 miles & feels stock NVH level on a warmed engine but cold engine still has higher NVH.
I’ve also previously tried VibraTechnic street mounts which had much better NVH overall except around 3000-3500 rpm, but the passenger side mount failed after 10,000 miles (with 6 track days) on a stock engine!
It’s a matter of personal tolerance, I’m most likely going back to OEM mounts.
There’s a reason BMW uses fluid filled motor mounts (European V8s seem to have too much vibrations). Experiencing NVH from BimmerWorld mounts, I now feel that it’s acceptable that factory motor mounts only last around 50,000 miles..

I went with Revshifts green poly mounts and there was a good amount of vibration and noise added. I replaced my tranny mounts with OEM at the same time. So just doing stiffer mounts will make a lot of noise and vibration. My valve train is more noticeable as well.

Extremely happy with my Powerflex engine mounts. Around same NVH as Vibratechnics mounts with none 9f the issues.

Hi everybody. Appreciate all the replies. I actually bought two gaskets that connect the primary cats (or in my case, the test pipes) to the headers based on this post (https://www.m3post.com/forums/showthread.php?t=1027393). I have a feeling mine might be shot as I've been experiencing similar issues. When I'm in there I will check all heat shields/mounts to see if anything is rattling. They're supposed to be delivered tomorrow so I will report back. If everything checks out down there, then I guess I'll chalk it up to the mounts needing some time to wear in. I've only had them on the car for about 100 miles.