I think I have the same deal with my passenger window. The guy at the body shop that will be fixing it told me that the window motor is essentially designed to fail. With that cable moving up and down so often it has the same effect of rubbing a metal cable on a pane of glass. it cuts right through it. Eventually the cable doesn't wrap around very well anymore because it has dug itself a hole into the motor. I am having mine replaced for $137.