Some really good advice here,and some good bike carriers too, I have a Swagman that is rated for use on a RV. What some of the problem is that they bounce a lot and if the rack is not tight in the receiver that added movement only amplifies that bounce.
I have tried almost every Anti Rattle device on the market, most have been no good or so complicated and cumbersome that they are useless. I have a whole tool box full of them.
Until I found the one at Hitch Rider. This will keep everything tight.
Their
Hitch Vice is the best and easiest one I have come across and it really works.
I also use pool noodles that are split to put around any part of the bike that may come in contact with another bike or the rack and use velcro strips to keep them on,pull them tight and press.