I'm a big fan of the FrontRunner quick release tent mounts. I don't have any rattle on my rack when it is mounted. Although your tent will sit up a few inches higher on your rack if that is an issue for you.
But frankly I am surprised you are getting rattling if you are mounting directly to the rack. I figured that would produce even less vibration, but I guess I was wrong.
I do like to remove my tent when its not in use so the quick release tent mounts were ideal for my needs.