I just bought an 04 GT Convertible and noticed there's something funky going on with the Mach 460 system. I noticed it because I heard muddy bass response from the back of the car. It bacame obvoius when fading between the front and back speakers. The front speakers appear to be fine (if not a bit Treble heavy), but the rears are super muddy sounding, as if they are both blown. I have yet to take it in for a warranty visit 'cause I'd like to feel confident in what might be the problem before I go in. Would it be the speakers or the power amp that's gone? Any help would be appeciated