It is actually a small number of things. Try shotting some spray silicone down the rubber chutes in the window rails. This will loosen the grip the rubber has on the glass and allow smoother passage. This is only temporary though. A few other tips have been given on the VMag forum you may wanna try out, like shimming the rails. There is also a supoosed UNofficial factory fix for it, but this has yet to be proven I believe. Good luck.