did you ever stop to think that your processor or your CD that you use has noise in it that the SD amps pick up ? maybe you have low RCA voltage due to the HU/ processor makeing somthing weird not all amps are made the same some are more sensitive to peoples setups more than others. you think that when you took the amp out you didnt change something to make that noise from the proto to the production amp?
on another note i think SQ is stupid why would you be that anal about a car you drive? home audio i can see but its just music in a CAR drive your car if you hear the noise at 60MPH yea maybe the amp is picking up noise or you have a poor electrical system or you just **** at diagnosing noises they make noise suppressors for a reason