Originally Posted by
AllGo'n'Show
Have you replaced the diff anytime in the last little bit?
When you swap one diff out for another but keep the same gears in there, atleast this is true for domestic modding, haven't looked at a BMW diff but pretty sure they all the same design, anyways... if you keep the gears but change the diff out, you have slightly changed the telerances and clearances of bearings, location of the diff to the gears, therefor when the gears were first put in, the worn down in one spot on every tooth, making smooth mating surfaces, no noise. If you change the diff, then it may be out by just the tinyest bit cause that worn spot to no longer be the place of contact, creating noise, creating a whinning.
If thats the case, no problems, just noisey.