System woes...Please help

I am at my mind's end, and need help PLEASE!!!
I have a Rockford source unit with front and rear pre-amp outputs driving a 4 channel Nakamichi amp. Channels 1 & 2 on the amp drive all the speakers inside the car, and Channels 3 and 4 drive 2 Nakamichi 8" subwoofers that are bridged.
Question 1. Intermittently, the speakers in the car give a little chirp. There is no pattern to the noise. It just gives a little chirp and then the music continues to play. The chirp lasts less than a second. I thought this was the amp. I got the amp sent to the factory and they said that it has no problems. Ideas???
Question 2. I was thinking of wiring a second amp, a simple 2 channel amp to drive the subwoofers, and drive the rear speakers on Channels 3 and 4 of the Nakamichi and front speakers on Channels 1 & 2. This would give me the ability to fade front to back. Do you think this is worth it, or just leave it alone?

Please help!!!
Thanks.
Raghu
91 300 SEL