The most likley part is the regulator. I had to replace this on my drivers side. The regulator has three mounting points. On my car on both the drivers and passenger side the two attachment points to the door had given up, that is the regulator was not attached to the door at two points. This causes the regulator to twist as the force of the motor is strong. I think that the motor is too powerfull and the attachement points are weak. A flaw in the design. Expensive part as it comes in one piece.