squeaking windows...

Everytime I drive over bumps my back windows make a loud squeaking noise. It's pretty annoying. Has anyone had this problem and figured out a way to stop the squeaking?

when I bought mine I thought my rear window was squeaking, it drove me nuts!!! one day I tried messing around with the window and came to realize it was the rear seat bracket on the passenger side making the noise going over bumps. It was So Annoying!! I tightened the bolts and no more noise..
Just an idea, I really thought the noise was coming from the rear passenger window.. till I played with it
-Jimmy

thanks, I appreciate your reply.