I can feel the thunk when it occurs, it isn't a minor rattle per se. Will try the brake trick.

I have a lift but want to know where the best point(s) are to jack the engine to determine a bad mount.

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1999 E320 (gave to daughter) 250K
1994 F150 (may be the end of its road) 240K
1989 560 SL (Reassembly after paint job) 160K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (still running strong with an upgraded cam) 349K
1986 242Ti (deceased)
1968 GT500KR (under restoration)