It is difficult to determine what is causing a rattling noise without actually being able to see the vehicle, but I can give you some tips on where to look if you are comfortable crawling under your vehicle to look at the hitch.
The alternative would be to take your vehicle to another local trailer hitch installer to have them inspect the installation. If you are anywhere near Wentzville, MO, we would be happy too take a look at it for you.
If you are comfortable looking under your... view full answer...