Originally Posted by RimasRS
I know that even M3 bushings already gives more vibration and noises to the cabin.
This was certainly my expectation. Intuitively how could they not given how much stiffer they are than the originals? In fact though, I can't tell the difference in terms of NVH with the M3 bushings. When I made the change it was the only change I made at the time. Others who may have made changes to the rear bar, shocks or springs at the same time may have a different experience, but it may be from those other changes. A far bigger contributor to the NVH quality of your ride is your tires. NVH should not be a reason not to change your rear subframe bushings to the M3 bushings. I have no idea if this is true of plain urethane bushings though.