the subframe on my 2011 E93 was recently damaged from a bad differential bushing, so i ended up swapping out the whole rear subframe out with another one from an used BMW M3. In the process i decided to go with Solid aluminum bushings for the differential and subframe.
the reason i chose Macht Schnell Solid aluminum bushings was because they were in stock at EAS. I have driven the car for around 200 miles so far, and there is a definite increase in noise. it is the differential whine noise. it is a little annoying with the music off, but.... i usually listen to my music really loud. i knew this was a possibility going with solid aluminum DIFFERENTIAL bushings. don't really notice any increase in vibration, or harshness. very daily drivable.
other than the whine noise, every thing else is fantastic. the car feels more solid, and the handling feels way better ( i also installed eibach pro kits in the process).
if i had to do it again, i would probably go with power flex, or the derlin/aluminum differential bushings. but i definitely recommend upgrading those rear differential bushings to something more solid; or at least keep and eye out for worn out differential bushings.
