I had the same identical problem in one of my cars. Noisy on bootup and rear channel buzz/static at low volume. Never chased it down because I assumed it was in my wiring. However, I recently sold the car and when I removed my Empeg and replaced it with an Alpine head unit, the noise dissapeared completely, even though the wiring was the same. Basically, I used the same power, ground, memory and RCA connectors on the Empeg and the replacement Alpine. I'll check the sled wiring on the removed Empeg and reply here if I find a faulty ground.