Mustangmaster

I have a 2008 GT/CS and about a year ago I backed into a pole in a dark non familiar area and it put a small bend in my rear bumper. I didn't have the rattle until maybe 2 months ago. I've gotten under the car trying to find the rattle and couldn't until today.

There seems to be bumper cushions in between the outside bumper and some steel just behind the plastic outside bumper. Near the ends of the bumper, I can feel the bumper cushions and they are loose. I feel sure this is the rattle that I'm hearing.

Has anyone else have this? How did you fix it?