You might try replacing the sway bar links. Mine sounded like I had a load of scrap iron in the trunk when I went over a bump. Now it is quiet. It cost $8.50 per side, and took about an hour. Remove the rear tires and you will see the links. They are plastic about six inches long and sort of "S" shaped with a rubber bushing at each end. If yours are worn out, the rubber will be completely missing. You will need two 17 mm wrenches; one must be open ended. Good luck.

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Bruce

73 220D (never left Germany)
81 300D (totaled)
84 300D (Purchased '03, sold '17)
85 300SD (purchased 10/01/03)