probably a quarter stuck in the rail. happen to me in my cl onece nad i couldnt move the setas for months and the i tried out of te blue and it moved. look under the seat and there was a bent quartslaying ont he side of the rail.

 

I was going to mention this too. Coins and ballpoint pens fall in the railings and jam the seat back. Once I had the wired remote for the iPod wedge in there and it was real pain getting it out.

 

HAHAHAHA...that was hilarious