Rear wheel bearings are permanently lubricated sealed double row ball bearing units, they cannot be serviced. Replace if they go bad (usually grind, groan, or thump). By the time they get play in them, you've noticed other symptoms as well!

Dif noises usually change with load, but not always, depending on what is wrong.

A professional hands on opinion wouldn't be out of place here, you are talking some bucks.

I don't know if you could get a lower ratio that 2.65 for a diff, that's the lowest I've ever run across! Our old Oldsmobile was 2.76 -- talk about a scary car! 90 mph upshift into third on the automatic, top end around 130, and NO brakes to speak of.....

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!