Had same problem when we first pulled out of the Casita
factory. (Draw-Tite hitch, Infiniti-dealer installed). I called the great service guy at Casita
. He said "call Draw-Tite, they'll take care of you."
Draw-Tite came through and free of charge sent me one of these:
Note that the hitch receiver must be a compatible two-hole J-pin type like the Draw-Tite shown (scroll down) in the link. I don't know whether other hitch brands have the two-hole config.
No more clunking. Thank you Draw-Tite!