03 Celica GT-S stereo problem

[multarnc]

I seem to be having a problem with my stereo. It is the stock JBL system. I bought the car Certified Used about 2 months ago. I was playing with the fader when I realized that the back speakers are very weak. There is little to no low or mid range. The front component speakers sound are working fine. I don't know if the problem is in the amp or where to start looking.
Any help would be greatly appreciated.

[Luc]

If it's certified used, take it back and have those lazy bums fix it. Those tests are a joke, nothing but going down the list and checking it off. I once found a cracked windshield and VIN covered from "certified" used cars at a Lexus dealer!!! Unless the car has over 36,000 miles on it, you should still be under warranty for an '03.