use an anti-rattle plate/bolt between your hitch and adaptor. Like this
View attachment 251754
I have an extender from my hitch so that my bikes don't hit my spare tire mounted on the rear of the vehicle. It did the same thing until I installed the above. Drove me nuts. You can get ones that fit both 1 1/4 and 2" transition adaptors.
This one fits the 1 1/4 to 2" transition because it has a larger flange.
1-1/4' to 2' Anti-Rattle Clamp for Hitch Receivers -Reduces rattling noise and movement -Fits 1.25' or 2' receivers -Keeps Hitches and Accessories quiet and stable
www.fayettedistribution.com