Explorer: Noise drivers window

I have a 91 Ford Explorer 4 door. It has power windows and when you lower or raise the drivers window it makes a screaching noise. It has never scrached the glass. I took the door panel off to look at the bushing and slides but didn't see the problem. Of course it is hard to see in there. I put grease on the bushing in the tracks thinking that might help but it didn't. Does anyone know which bushings are bad to point me in the right direction. Thanks You might try a very small amount of WD 40 to the inside and out side felts, that is the black rubberish part that touches the glass. if that does not help you might need a new window motor.Car Repair Talk's forum.