sealed enclosures

Systems

I re-did my subs enclosures, let me tell you sealed or not, I am very pleased with the sound!!!! Now my next dilemma. I have a PUNCH 400a4(i think) pushing the subs. It is plenty of power but,when I turn up the gain I get lots of noise or feed back!!! This amp is for 4 channel at 2ohm or 2 channel(bridged) 4 ohm instal. I'm risky, I know, I'm running it at bridged 2 ohms!!!???first, how to get rid of noise?? second How much power is reccommended? subs are polk DB 10's. I want to buy a 2 channel amp. p.s. when I turn the gain on the amps down the noise goes away, or when the amp is at the right resistance per channel there is no noise!! please help, noise and wattage problem , thanks Boris...