Greetings,

I think I'd check out a few things for wear to isolate the problem. First thing that comes to mind is the driveshaft support rubber as well it's mounting bolts. I'd next look at the flex disc on the rear differential and lastly if all else fails it could be a half shaft on it's way out, but the sound wouldn't necessarily be a thumpping sound but a consistant whine or grinding sound coming from the rear. Does it sound like a thump coming from the driveline tunnel when it happens?


Charles

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'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan