2002 GT noisey interior

I have a 2002 GT coupe that at freeway speeds sounds like a window is open. The noise seems to come from behind the front seats, like maybe the back seats are not making a good seal. I bought it new, and this has been a problem since day 1. I've had it checked out by 2 dealers and they both say the noise is within specs. Does anyone else have this problem, and/or does anyone know what to do to make it more quiet? I've already blown out a speaker because I have to turn up the volume so high to hear the radio. Thanks for any input.