Print ASA or TPU 100% infill.

Works best when sandwiched between existing rubber and steel anti-rattle spacers.  If your hitch doesn't have a pre-load screw for loading the spacer after installing the cross pin, you will need to leverage the hitch into position with a punch.  When the pin is installed, it should be tight to get best results.  

Or print minimum 6mm thickness ASA for both sides, with middle part TPU with varying infill (35%) to add compression.  

Minimizes hitch rattle.