Bump this back towards the top. This fix DOES work. I took a print-out to my SA and said just do this. They argued a bit about it and said this was not an official fix for the rear creaking/popping, but I was firm.
A day later I picked up the car and it is SILENT! Woo hoo!
It's now been about 3 months and it is still quiet, all the way from 20F to over 90F.
If you've got this issue (and I think all 3 series do), just print out this thread and tell them to try it...
-Michael