When pass. side window is 3/4s of the way down it makes a matalic sound and the window jumpes slightly.I removed inside door panel to check the motor and regulator teeth and all is o.k Looking at this area all is operating smoothly.I can not see any problems with both tracks and cannot pinpoint where this problem is.I did however notice scratches on the outside of the window on the door handel side.Very confused! 1989 420 sel