I read that as "war page" at first on the thread :lol glad that its only warping.
I've seen that on a couple of cars... mostly 05's if memory serves me correctly and higher (more than 2000) miles. All had stock exhaust and no spacer between license plate and grill.
Put a couple of spacers (or nuts) between the plate and the grill to help get the heat out of the back end. Fixing it .... probably new rear part (call the GT guys about it).
Myself .. I'd just leave it as part of the Patina (as Shadowman calls it) of use. Change the exhaust and enjoy. Every pretty lady has her quirks that we grow to love as part of the total package.