Mine does this and it drives me nuts. I can't find the source of the problem and my parts truck has the same problem. I wedged a piece of wood between the moving parts and that solves it, until the pice of wood falls out.

 

This happened to an old '04 of mine. Truck was still under warranty so I brought it back to the dealer. I think it happened twice. Each time they said they had to replace some part of the frame or the frame itself. Sorry, not much help, but it seems like it might be some sort of weld that breaks on it.