2006 Ford Explorer Best way to get repair completed

Hey guys,

I got rear-ended a few days ago and it did very minor cosmetic damage to my vehicle. She hit my trailer hitch and rear bumper with a Chevy Cobalt. Since it happened my rear-end has been making noises like metal rubbing against metal everytime the vehicle's weight shift's from one side to the other (turns, quick stops or accelartion, going over speed bumps diagonally). The only visible damage was to my rear bumper though.

I am positive this noise was not happening prior to the rear-end collision. I took the vehicle to insurance adjuster and they gave me and estimate of $500 saying nothing was wrong with it except the bumper. They are also fixing it and gave me a rental. I am not sure what to do and am concerned that this problem will continue. They said if I take it to my own mechanic and they find the problem and it is related to the accident it will be covered. Any idea on what could be wrong with it? They didn't drive it but lifted it up to take a look underneath it.

Thanks!