I'm having this problem of squeking sound at the door for my new 5 Series. When I sent to AB this afternoon, there was another car also having the same problem but at different door. Mine happened at the rear left door. That guy's problem was with the front door. Seemed that it happened due to insufficient lubricant applied to the door lining causing it to have some leakage thus squeking sound when the car is in motion. Those having similar problem should send back to the dealer for repair. Not a good QC control at BMW factory it seemed.