Potential whine from rear wheel

[mojoguzzi]

Dealers don't check or grease the rear shaft splines as part of normal maintenance, as BMW doesn't recommend it... even though owners have observed rust on on under-lubed splines after less than 16K miles.

I had my dealer do exactly that 4K miles ago.

UPDATE (a bit): Changed the final drive oil--no bits, no bright metal flakes, just normal sludge at 4K on that oil. Will ride it tomorrow (things got in the way). Have an action camera mounted near the FD. We shall see.

TIA y'all