Ah, just found the post...
No whine. (perhaps a cabernet, though?)
36k miles.
I am sure you will hear comments to the effect that many SAs use the "they all do that" excuse when they don't want to get into a mess with warranty claims and BMWNA hassles...
E39Mfive is dealing with a whine if I recall.... a few others have as well.
road speed or engine speed related? Only under acceleration? I only ask as I know these are important discriminators for tranny versus diff.
If you are still in warranty you MUST get this complaint, with as much possible detail, writtten up on a work order. Just talking to the SA who dissuades you from proceding will do no good if there is a future failure. Even if they write it up, and reply "no problem found, normal for car" it might be important
My 3 cents
A