I wired a rockford fosgate 200s parallel recently to two 4 ohm 15" Pioneers. When i turn it up to a certain a volume the amp shuts off momentarily until i bring the volume back down. The power cable is connected to my battery and i have the stock alternator in my '99 Cavalier. Is my amp shutting off b/c it is draining too much power? Do i need an external battery? Any help is appreciated.