Time for the 4 AP's. Raise the rear of the car safely and use a pry bar to Push, Pull, Pry & Prod on all suspension points to find where it's loose. Subframe mounts and control arm bushings would be likely culprits.

Good luck with it and let us know what you find.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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