So, how much noise from the diff is too much noise? I know, a very subjective question. (And I did do a search on this subject). The car has ONLY 352k miles on it, so I expect a few noises. But cruising along at about 65 mph the other day, I did hear what I don't remember hearing before. A definate drone coming from the rear, which is only there under acceleration, but goes away when I let up on the gas. It's not real loud, but it's there.
Keep driving? Or get it fixed?

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)