Rear speakers not working in 2000 GTP
 

The rear speakers in my 2000 Grand Prix GTP aren't working. Also, I swear that the "fade" knob turns the wrong way.. By that I mean what I think should be "fade to front" actually fades to read (even though I can't hear them), and "fade to rear" has the front speakers coming on.

The front speakers also sound "boomy" like they are getting too much bass even when listening to non-bassy music.

I can't give a whole lot of details since I just got this car today with only 36,000 miles on it. I called the dealership as soon as I noticed it (my test drive was focused more on mechanicals of the car) but they are an hour and 45 minutes away from me, so I can't just swing by. I'd like to have an idea of what is going on so that I know what to expect them to fix.

Thanks!