Sorry I didn't see this thread until now. I will tell you that I had the exact same problem!
I actually already posted about it, but it got buried in a thread.
My symptoms were:
- buzzing sound/static noise when brake pedal depressed
- engine noise/whine
- all through only ONE
MS-8 channel (center)
It drove me crazy and I got to the point where I was going to tear everything out, everything! None of the traditional trouble-shooting steps for engine noise worked and the brake-light buzz gave me nightmares, literally.
I double, triple, quadruple checked all the wiring for the center channel, to make sure there was no interference being picked-up by the wires. I even ran new RCAs and speaker cables for the center OUTSIDE the car, and there was still noise!
It was actually just dumb luck that I found the source of the noise. It is not anything I had ever thought could possibly cause this problem, since it was just one channel and not all of them.
Here's a couple of pics to illustrate what was going on:
I originally ran the ground cables for the amps parallel to the RCA as shown in the
picture. There was about 1/2" clearance, but the RCA plug (on the HD600/4 amp) for one of the underseat woofers (CH 3 or 4) picked-up the noise from the ground wire, then back-travelled into the processor, and then magically reappeared on CH 5 (center) output of the MS-8 and went through the RCA back to the other amp (HD900/5).
As soon as I unplugged the RCA cable from the HD600/4 nearest the ground cable, the noise stopped. So I just re-ran the power and ground wiring AWAY from any RCA plugs and voila, problem solved!
I hope this helps you but at least it shows that the cause of the noise is not always something logical!