95 S420, diff. whine, or Rear wheel bearings?

[DanielW]

What would be the most likely cause for wear of this kind?
I had changed all fluids (including the diff) when I purchased it from a MB dealer at about 51,000. Used Mobil 1 synth. gear lube 75W-90, (the best I knew of). All was quiet until about 82,000 when a small whine started at real slow speeds (and at 85 up). I changed that diff grease again yesterday, and found small amount of very small bright metal tiny particles in the drain bucket. I kept everything clean so I could see what was there. The lube was still bright, and smelled just like the new. It was practically clear, (as is the new), but there was enought metal I could collect some with a magnet.
Present mileage= 84,406 and now it's whining badly.

I believe this should be a covered repair since it's still under the Starmark for a few more months.

Dealer had done a "differential re-seal" for the PO at 48,000 under the orig. warrantee. Is this very common?

A few days ago , I had thought it could be a rear wheel bearing? Service writer says they almost never go out unless rim is hit hard---that has not occured. What about CV joints on rear? But the grease seals are unbroken and do not leak. I thought those usually are good unless they loose their grease?

I have an appointment Thursday. Any experiences along these lines would put me in a more comfortable position. Educate me QUICK. Seriously, I would appreciate knowledge from those "in the know" by experience or training

DanielW