I also have some noise emanating from my rear end (240D), so I'm finding all this fascinating. My car is just generally noisy, but no vibrations or rumbles so far. I have not even tried to diagnose anything yet. I've never even had my car on jack stands.

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1979 240D, 4spd manual, Power Sunroof, manual windows, 147k miles, Pastel gray/Black MB Tex.
1991 300D 2.5 - Smokes like it's on Crack!