"Clunk" on reg cab rear??

I am taking my truck to the dealer today to let them look at it. I have seen the squeaky leaf problem many are having but I don't think this is it. When I drive over a normal sized bump I am hearing a clunking sound. Also I can stand on the rear bumper and jump to simulate a load and it makes the same sound. Is this the suspension bottoming out? I tried to get something out of the dealer and one guy hinted like it might be a warranty fix but what do you think? I have the platinum warranty so if it is I should be covered (hopefully). I live so far away from them I'd hate to waste a trip.

 

Bump before I head out to the dealer