Bed making a rattling noise going over bumps

My truck sounds like it has something bouncing around in the bed when I go over bumps. Do the 1st gens have rubber bushings on the bed mounting bolts to deaden sound. If this is true, does anyone have a part number for the rubber bushings. It's not critical at this time, just annoying as hell.

 

Last bed I took off had 6 bolts holding it down with the two near the tail gate having large washers. I would check all the bolts first and see if any have backed out.

 

I don't remember any bushings. I've had the beds off of two 1st gens.

Could be other things loose, but easy way to diagnose bed: put some weight in there and see if the noise goes away. If it still makes noise, move the weight around to each corner and see if/when it goes away.

The bolts can be checked of course, but they may be rusted and feel tight. You could probably tell just by lifting at the corners and see if you feel any up/down movement at all, but not trying to be funny here, I didn't know if you are able based on your user name.

Edit: If you really are a "Crippled Old Man" and want to diagnose with some weight, here's a method. Go to Lowes/Home Depot and buy a could bags of concrete mix. They'll load it for you. Drive around a day or so (not in the rain ) and then return the mix. They'll take it back.

 

check the 2 exhaust heat shields. My money is on one of them is rattling.