2001impala is on the right track. You can stop worrying about house wiring right now by what you've already told us. Your house wiring is innocent because the problem is somewhere between preamp and power amp, which you can tell by changing preamp out-->amp in connection and following the buzz around by doing that (at the same time, your other channels are fine - which means that wallpower into the preamp unit and amp unit is fine, since if it was bad, you'd hear something elsewhere).
Again, I suspect the cable. Swap it with one you KNOW works. It's okay to run the amp without input on some channel inputs, and to run the preamp without output on some channel outputs.
If different cables don't clear this up, it's possible that the center output jacks on the preamp, or their connection to their host circuit boards are damaged.
Again, I suspect the cable. Swap it with one you KNOW works. It's okay to run the amp without input on some channel inputs, and to run the preamp without output on some channel outputs.
If different cables don't clear this up, it's possible that the center output jacks on the preamp, or their connection to their host circuit boards are damaged.