I Need Help

Hi All,
I recently purchased a used Denon AVP-8000 along with the matching amps POA8200 & POA8300. I was told that this thing was just like new. Yea it looks good but not playing like one. I have experienced a buzz, very low but audible, from the center channel only which also gets louder if the unit is played for a extended time ( I think, for you see, Denon has had this longer than I have and I really can't remember). I do remember my wife is ready to kick my ASS if I tear this house up one more time rewiring and etc. It has been to Denon service twice since May and they have not fixed a thing and I have just sent it to them for the third time about 3 weeks ago. First they told me they replaced boards inside the unit(3 of them to be exact) and said it was OK. Hooked it back up and the buzz was still there. 2nd time they replaced another board and said it was fine and guess what?..same buzz. I have done about everything imaginable and now I am lost. Spoke to Denon yesterday and they are going to look at it one more time. They have been looking for 3 months now and still can't find the problem. I was told by them that this noise may be generated by house current and/or may be normal and that all digital equipment has some type of noise generated through the outputs.Swirling, hissing, warbling... PLEASE! If that's the case then why aren't all the speakers buzzing? It is only coming from the center when played in any 5-ch. mode.If I move the center channel output from the pre amp and plug it into ...say right rear input of the amp..the buzz goes to that speaker. Am I missing something? Is there a problem in my house wiring that could only be triggering the problem out of the center channel only? I am using Klipsch R-3 series center and surrounds if it makes any difference.
You might have a bad interconnect.
I had the same annoying buzz in my center once. It was like the ghost in the machine and was very difficult to find the problem. First I would recommend that you hook the center output up to one of your mains and see if it still buzzes. If so, then at least you know the problem is not the speaker. Next, try unplugging everything except the center channel and some type of source (if you can get by with the radio in mono, this would be best as nothing is connected). Then, one by one connect things, and see when the buzz returns. Chances are you could have a ground loop, and this could tell you where the source is. Once you find it you can either lift the ground or change the ground to hopefully remove the loop. Hope this helps.
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.
Do this:

With the power OFF for all of the amps except for the
center channel - listen... IF it is still buzzy. Unplug
from the wall, each amp's AC plug and see if the bzzz goes

alternately, take the center channel output with the other outputs NOT connected at all and listen.

IF still there, disconnect ALL the other inputs to the device that is generating the 5 channels of junk sound and see if that makes the buzz go away.

IF it is still there, unplug the digital transport that is the source (and/or turn it off.

Point being this: IF it creates the buzz in the center channel in the 5.1 channel mode by ITSELF then it is not any sort of cable or ground loop.

The idea is to systematically eliminate everything one step at a time to isolate the causal factor.

It very well could be ground loop or simply bad decoding with digital noise in it (a defective circuit).

IF it is still buzzzing with nothing but the center channel amp connected, then try that output with a left or right channel amp connected to it. That will eliminate the amp from consideration IF it still buzzes, and if you use another interconnect (just swap it over) then the interconnect is not suspect either...

Thanks for all the responses so far. I will tell you all that at one time or another I disconnected EVERYTHING but the antenna for FM. I hooked up my old Denon 2-ch. amp (POA1500)to the AVP-8000, right lead to the right main speaker , left lead to the center and the buzz was there in the center speaker. I even disconnected the FM antenna,hooked up nothing at all,turned on the unit with the old amp then the 8200 & 8300 amps and the buzz was still there. Possibly a bad interconnect. I am using Monster and I wonder just how good they really are. Spoke to Denon tech advisor today and he told me that they connected a speaker(a small one he said,did that matter?)to the pre-amp yesterday and he and the service tech heard nothing at all and they are convinced that it is not the pre-amp that is at fault and they are ready to send it back. He said with the new boards installed that the unit was really clean and quite. I still feel there is something wrong inside and they don't know how to fix it.Stay tuned for more to come and thanks again for the replys and will keep you updated.