Yes, in certain circumstances you can hear the diff with solid subframe bushings and Powerflex purple diff bushings.
Windows up, music off.
My brain has finally filtered the whine out after 7 months.
The improvement in the car's behavior on track is absolutely noticeably improved though.
Well worth the expense and effort.
I added adjustable sway bars while I had the subframe out of the car, so I was into it for around $1,200 for parts.
Subframe bushings, $275
Powerflex purple diff bushings, $161
Hotchkis sway bars, $490
Braided brake lines, $161
Plus various TTY bolts and brake fluid
https://www.bimmerpost.com/forums/sh...php?p=27648714