problem with subs

I have a very frustrating problem with my subwoofer in my max. I have one JL audio 15" sub that had a coustic power logic amp and crossover. I was running this setup for at least 6 months with it sounded excellent. One night I was driving and my sub just goes nuts, it just pumps out base in this one tone that sounds like feedback? maybe? I was told it was the crossover by multiple people. So yesterday I went and bought a new rockford fosgate amp. I hooked it up and what do you know? same problem. So I proceeded to do a quick check on the wires in the car which all seem fine. The wires connected to the sub inside the box also seem fine. If anyone has any ideas or suggestions please post them.

Do you hear any popping or crackling?

What is the RMS on the old AMP and what is the RMS on the speaker?

I can probably help you out, but, I need more info. What exactly is it doing and tell me everything you have connected?

thanx for your help guys but I have since fixed the problem. A friend of mine pointed out that since I still have the stock deck in the car that the back speakers cannot be hooked up in parallel to the amp. That is what was causing the feedback.

Cool! Keep the soundz bumpin'!:D