Don't know where to start troubleshooting this sound problem...

....and it's actually a little hard to describe. I've got an OEM stereo in my 01 1st gen, with the 6 speaker set up (4 in the doors, 2 in the back) with a USAspec unit hooked in so my Sirius Sportster is hardwired into the system, and I can plug my MP3 player in also.

It's starting to act 'weird', the headunit itself has some issues now and sometimes doesn't want to switch from radio to cd to aux input, I'm assuming that is the head unit and there isn't anything to be done about that other than buy a new unit. The weird problem is with my sound, every now and then I'll go around a corner or maybe over a hard bump and all of a sudden it's a different quality, like the bass wasn't playing well and suddenly it's back. Where should I even start with this?

 

Try taking the plugs out of the usa spec unit and let it chill for a few mins. Reconnect and see. Obese having some probe with my USA spec iPod unit. The above solved everything.

 

I've let this sit for a while trying different things and trying my best to troubleshoot things. I enlisted my wife to help and finally figured out the sound moves side to side but neither side is entirely silenced. It basically seems like, for no apparent reason at all, the sound will be reduced in volume and fidelity and also seems to shift to the left side a little bit. I have shifted the sound using the headunit so it plays in each individual corner and none of the speakers are broken or non-functional. Like I said above, my stock JVC head unit doesn't work all that well, but also my USA SPEC is about 6 or 7 years old now. How do I figure out which one is the cause, or how do I eliminate either one? I know the easiest way would be to just unplug the USA SPEC and see if the problem still exists, but my radio button stopped working and won't switch and the tape player quit working a few years ago.