Here is a thread, (and there are other similar & connected ref threads);
http://www.xoutpost.com/bmw-sav-foru...ing-noise.html
And, a general list of possible relevant threads:
Xoutpost.com - Search Results
5 sec hunt using Search Tab, and a couple mins of reading through the relevant
threads. Slip ring/clockspring parts seem to be the culprit, though I remember
some posters using a silicone based spray to alleviate the noise, for awhile.
GL,mD