Audio Systems: Sound Problem

Question
Hi, I have recently been having some problems with my car audio. I drive a 2005 Chevy Cavalier. I have dual 12" subs  running off of a 500 watt amp. My head unit is stock so i have hooked the imports to my amp to the wires going to my back speakers.

The problem i am having is that when I turn my subs on with my toggle switch they may stay on for a while if my volume is low, but if i try to turn the volume on my head unit up all sound from all speakers stop. The head unit still has power and seems to function as normal but no sound will come from anywhere. If i go to my trunk and unhook a wire from the back speaker wires going to my amp everything will turn back on and i will have sound again.

Also sometimes while playing music even without my subs on the sound will stop playing my music and a very loud high pitched ring will play through my speakers. I can turn the volume down and even push the volume adjustment knob in (usually stops all music when car works right) and the high pitched noise will continue to play. The only way to get the noise to stop is to shut the car off and open my driver door.

I plan on replacing the head unit no matter what because I would like an aux port (especially because the cd player stopped working) and so that i may properly hook up my subs.

Would replacing the head unit fix this problem? Or is there something else that i need to replace while im doing upgrades?

Answer
I'd need more information to give you  a more precise reply but my first guess is the overdrive to the sub amp is the root cause.  If you are connecting speaker level output to the input of the sub amp that audio level is too large for the input circuit on the amp  (Unless your amp has a speaker level input; some amps do buy not many).

The squeel is likely coming from a feedback condition which usually means you have a bad ground or the interconnecting wiring is routed too close between inputs and speaker cable outputs.

I don't think a new head unit will help unless it has low level outputs to the sub amp.

You can acquire a hi-lo adapter from Installer.com and others. That may be a good solution.

http://www.installer.com/main.php?page=hilo

Cheers.