How to I keep my car speakers from rumbling?

I have a Pioneer DEH-P5000MP deck that was hooked up to a Lightning Audio 600 watt amp. From there, I was running 2 6 or 8 inch pive Bazooka tubes speakers. About a week ago the amp got wet so i upgraded to a 800 watt Sony Xplod, then tried to hook up a 10 inch Alpine Sub to it. This caused the amp to overheat, so I unhooked the sub. When I went back to hook up the Bazooka tubes the only sound that coms out is a rumbling with a little bit of distant sounding music. Thinking that my amp was blown I took it back, and bought a 1000 watt Kenwood amp, but this didn't change anything. How do I fix this rumbling noise?