First almost on any modern car if you don't see it, it is in the back window.
I just fixed my 06 GT, FM was acceptable, but AM was bad. Turned out to be the window tint. The older tint has metal in it. I just bought a 07 GXP and had it tinted, that was when I learned about it. Also one place said I had to go ceramic, but the place I had it done said most newer good quality doesn't have to be and they were right. If that the problem, bad news it cost as much to have it removed as it did to tint it. Also when removing the rear glass tint they have to be careful of defrost wires. Had it done on my 06 and all is good.
Of course there could be loose wires, bad radio and such, was just throwing out my situation.