I have a '97 740i and sometimes the front drivers side and passenger side windows open about 1 inch by themselves when the car is parked. The rear windows don't do this. I know that some BMW's have/used to have a function where the windows would lower briefly and then raise to create a better seal but, to the best of my knowledge, mine doesn't have this. This happens very intermittently and I haven't spotted any patterns as to when it happens.