Clunking noise on bed

I finally found my noise. I set my normal height on the air suspension higher and that took care of the bottoming out and hitting the stops. But I continue to hear a noise coming from the bed when going over street bumps. The noise can be replicated when I jump on the rear bumper and it seems to be coming from the composite bed. I have checked the bed hold down bolts and they are tight. Any thoughts on how to solve this noise?

 

Yes, very simple take your truck back to the dealer