Audio Systems: car stereo-amp trouble, thump thump thump, rca cables

Question
i hooked up my new stereo in my car using the same amp and speaker system. i used a wiring harness. my amp has 2 10inch piioneers out of he back of the stereo i have the 2 rca cable plugs. i hooked everything up and when i turn on the stereo or change from cd to radio i get a thump thump thump thump for about 10 seconds in my big speakers, why. is it my amp interacting with the amp installed inside the stereo or what, help please. i installed a pioneer super tuner III cd player, i already had installed a urban 500 watt amp with 2 pioneer 10s. they worked fine with the old stereo but it wasnt ejecting my cds good it was old

Answer
It is best if amps turn on before the headunit does, but this is not always the case in car audio systems with normal remote leads, which sends power [to turn on the amp or other signal processor] as the deck is turned on and generally, the headunit will 'beat' the amp to a full 'ready status' when powering up.
But the fact that it does it when changing sources tells me to look for bad grounds, first.
Especially at the amp and the headunit.
If those are securely attached to the chassis, a main ground for the vehicle could be loose. Of course, the headunit ground would be the first one to check.
Next, I would check the RCA connections and cables or try new RCA cables.

Good luck.

Jm