Bad transmission mount will cause a drumming vibration as the tranny thumps around under torque. Noticable only under acceleration, can be quite loud.

I'd personally do the engine mounts at the same time, I did on the 220D and the 280 SE.

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!