I have an 05 coupe AT.

Could it be the brakes? They still have a ton of life left in them but they're also the lifetime ones from auto zone so they can't be all that amazing I guess. Seems to be coming from the driver side and occasionally I can hear it from both sides. Suspension and everything is stock.

 

If you installed yourself, did you use a good brake grease on all of the moving components? If not, prepare for squeaks. I ran those for a hot sec, and they worked pretty good. Too much rear bias though.