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
				
					
						
					
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