Rear Window problem

[TechWrench]

On my wife's '02 X5, she told me that today, while sitting in vehicle with key in on position but not running, she heard weird noise from rear area and then became aware that left rear window had gone down on its own. It went back up with master control, but soon after it again went down on its own. When she got home, I checked its function, and found that I could duplicate the problem with engine running or off with ignition in on/aux position. The first time I tried to roll it back up, it stopped about half way, and went back down. Next time it went almost all the way up, then stopped and went down. After that, it went up OK the rest of the tries. I thought it was a one time glitch, until we went out in the vehicle a few hours later. After starting engine, the window started making short bump type noises, and it went down a bit with each bump until it was all the way open. I used the button to raise it with no problem, but it again started to make the noise and lower it self. When I raised it again, I set the rear window lock button on the master controller to on, and the window didn't go down by itself the rest of the day.

I did a few searches on this, and I didn't find any one with the exact same problem. Most window problems seem to be related to the regulator failing in one way or another. I have replaced the plastic clips on both front windows over the last few years, but not sure if the rears work the same. Since the problem seems to stop when the rear window lock is engaged, I am guessing it isn't a control or switch problem, but not sure.

Any thoughts?