I'm getting a driveline whine too, mainly off throttle coasting. I'm about to change my fluids in hopes to get rid of it. But, unfortunately, I'm under the impression that it will come back, and eventually the rear diff will grenade. I'll replace it with a used unit.

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'10 X5 35d- 279k mi, deleted and DUDMD stage 2, daily and tow vehicle
'01 330i- Drift car: SLR Super angle, BC coils- keep it simple
'07 335i 6mt - Sold @ 171k miles- stage 2 daily commuter for 2 years