We had some chucking that was coming from the hitch-to-truck-rails connection... we put squares of foam shelf liner between the hitch and the rails, and that took it out.
Of course, that also insulated the hitch from the truck's ground, so we ran into an electrical issue (the ground wire on the Ford plug is not sufficient for the current loading, so the hitch connection itself provides an extra ground to complete the circuit)... but we fixed that by connecting the trailer to the truck frame with some jumper cables.