[Yosemite Sam]

I'm sure ksanders is exactly correct with his diagnosis of your situation.

If the top of the grill shell is pushed back an inch or so, it will only make a tiny kink in the tops of the frame rails where the grill shell bolts on (almost unnoticeable without removing the grill shell for inspection).

An easy way to temporarily relieve the problem is to put a flat washer or two (on each side) between the grill shell and frame where the rear bolts go through.