I'VE RUN INTO A PROBLEM.

I just bought a 2002 Lexus is300 and it has a factory amp.

I went to install my Pioneer Premier CD/Mp3 player, and ran all the wires correctly (I even had a professional helping me) and we ran into a situation that has us somewhat baffled right now.

We had to wire around the factory amp because we do not have the JBL wire harness that hooks up to the factory amp. Well, the CD player was working fine. All speakers were working except one rear speaker. It had them skreeching! So we didn't hook it up. It was working. About an hour later...listening to music...mid-song it skreeches in the rear again.  

So I'm thinking its either 1) a pinched wire...2) mis-wiring somewhere...3)my speakers need to be replaced or my factory amp needs to be replaced??? I mean, i dont know. Can I just use my Kenwood 800watt 4/3/2channel amp to hook up my speakers to? i have 4 left and 4 right input/outputs for speakers on my amp...but i'm trying to bypass that as a "last resort option". And, also, I was thinking...Should I just go to eBay and buy the JBL wire harness for my factory amp? It's only $89.99 ----- I just wanna know why it's skreeching like it is. Because when we tested it, it worked. Then it didn't. We took that wire off, it worked for an hour almost....Now it's not again.

Can somebody please help me out with some advice?

I'd greatly appreciate it.
Thanks guys!  

I would by pass the on board system and make a new circuit with the 800w amp, so you eliminate any variables. The speaker may just be going out the door already. I would chalk it up as coincedence that it screaches the way it does intermitently. You can place it on another channel and see if it does the same thing or replace it with a working speaker to see if it's not that particular channel. The new circuit should knock out any doubts about the on board amp. They almost never work the way you want with aftermarket stuff, any way, and there's always residual noise from the engine because of the extra loads from the system on the stock wires. Play it safe and do what I suggest. It will keep you from having some diagnosis headaches. The Kenwood amp is more powerful than the on board amp, any way. The on board amps are only any where from 150w to 200w.