Hi, This forum's focus is mainly on the "vintage" Mustangs, IE 1964.5-1973. However a few members here also own "New Edge" 1999-2004 Mustangs and might have an idea or two if you provide a few more details.
I've not personally heard of a "classic" 2004 model. Just the GT, Mach1, and Cobra editions.
As for the actual problem, tires jump to mind first.