Originally Posted by adammb
I do notice that the buzz comes from all speakers but I mainly hear it from the center and side surrounds the most which are on separate amps.
What do you mean by a block diagram?
So I had this problem when I finished my theater and it drove me crazy. There was actually 2 distinct hums. I literally unplugged everything and started plugging them back in to see what I thought it was. There was one hum coming from all speakers, which was mostly due to the cable input. That was solved with a ground loop isolator. http://www.amazon.com/dp/B0017I3K9M/...60_cs_sce_dp_1
Then I was getting hum which seemed to only come from the front of the room, and mostly from my subs. Removing the "grounding screw" on the subs (As recommended by axiom) didn't remove the problem. I use XLR cables to my subs as well, which means I didn't need to make a special cable to test out if that was the problem. It didn't end up being the subwoofers at all! In the end, it was the projector's power plug that was doing it (The power plugged into my power conditioner through an in wall inlet/outlet extender) I also had a home theater PC hooked up at one time which also had a hum. In those cases, 3 prong->2 prog power plugs solved the issue. I know those plugs are bad in a lot of cases, but they worked. At one point in time I also plugged a computer monitor into one of my column outlet jacks to test my HTPC (my theater outlets are on one circuit, and the subs are plugged into that circuit) and as soon as I plugged in the monitor, a new hum was introduced!
A lot of times too things have to do with two different power sources (Amps, whatever) that are on two different circuits, and how they play nice. Any kind of COAX cable usually can be an easy culprit. Ultiamtely though, you have multiple amps, all of which connect sound through a common pre-amp. I fortunately only had one 7 channel amp, plus built-in amps in the subs. So disconnecting things one at a time until the hum vanished really helped me. (Removed each speaker one at a time, each interconnect cable, each power plug, all the way through the whole system and plugged it back in if the hum continued until I got it narrowed down. Remember to try and unplug ANY power cable plugged into any outlet which shares a circuit with any of your A/V gear or subs)