I did not have to this yet myself, but here is a thread that deals with window trouble. Unfortunately the pictures are no longer there.viewtopic.php?f=20&t=19269
From this I guess I would first lubricate the track without pulling the door panel. If that does not help I would pull the door panel and observe what it's doing. Then decide if something needs to be glued, tightened and lubricated.
Good luck and report your findings.