I do not have air suspension. The only seat bins are ones under the rear seat, under that folding board that can create a flat space when the seats are folded up. I initially thought it was that folded board bouncing, because it just kind of flops around there. But, I had my boys hold it still while going down our bump road and it did not eliminate the sound or change it in any way. One bin has the amp for the Alpine sound system. The other has a tow strap and some stuff but nothing that would cause this level of clunk. You can feel the clunk when in the bed bouncing it. Again, only bouncing the bed an inch or so up and down. The only thing in the bed is a spray on liner and a very thick bed mat. But, it isn't bouncing. I don't keep anything in my hitch receiver. The hitch was factory installed. I'll try letting the spare down and putting it back tight. I'll try holding more parts, including hitch, while getting my son to cause the clunk to see if I can narrow it down more. I'll try leg pressing the bed to see what happens. I'll report back once I get a chance to do those things.