Ditto above...if it's not due to someone accidentally activating the convenience open feature on the remote key...its more than likely the window regulator.

The same type of thing happened to my front passenger window in my 99 540iT just before the window regulator gave up the ghost. It would lower itself a few inches...I'd raise it up...then over the course of a few days...or driving over rough pavement...the window would drop again.

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