621i noise

My '08 621i has a loud rattle, not apparently synchronous with anything. Smooth or rough roads don't seem to make a difference. It sounds like it comes from the right side, tho I can't be sure. I jacked up the rear end and ran it with no noise. I suspect an assembly right behind the passenger seat. It contains a coil spring, connected to a cable which goes to the lever controlling the differential lock. The spring is very loose inside the assembly. I tried padding the spring with a rag and an elastic cord. A short drive was inconclusive as to the effectiveness of the fix. I will have to drive it a bit more to know for sure.


Three questions: Has anyone else experienced the noise? If so, what was the cure? Also--what is that assembly for?


TIA