Things that go BUMP in the night
I had a similar rattle that only ocuured when I would hit a sharp bump at low speeds. It turned out to be the foam blocks inside the rear bumper
(these are the impact absorbtion blocks) My car is a 124 so I don't know if the bumper on yours is constructed the same. It took me three years to isolate that clunk as it didn't happen all the time.
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