Thought I'd 'resurrect' this thread as I'm having the hum/buzz from my 7500. Never noticed it before, but now that I've moved my amp I notice it. Starts as a cyclic hum/buzz (softer to louder) then after the amp's on for a couple hours it's at a constant level that you can hear when the volume is muted. Amp is cool as can be, and no noise from the speakers. Is the only 'fix' a ~$300 filter (either PS Audio Humbuster II or the Channel Island XDC-2)?

That is what I had to do to take care of the same problem with my 7500.
I tried different outlets, unplugging the fridge and other electrical devices but to no avail.
I went with the CI XDC-2 and all of the problems went away.

That's what I figured I might end up going with, but when I showed my wife a pic of the CI filter and told her it was $300 she about stroked. I was hoping there was another 'cheaper' possiblitiy for a fix out there. I didn't have this issue with the 7125 or the 7075. Apparently it can be a common issue with amps and residential A/C service, but it's kind of sad that you have to spend another $300 to 'fix' a $1,500 amp.

I feel your pain.
Outlaw was going to start selling a DC filter but I am not sure if they ever did but you might want to call them and ask.
You would think they would have a better price for their customers.

I will give them a call and check, but I'd guess if it was a product they offered it would be on the website. Probably one of those things that would be nice to offer, but not a big seller, so it was never developed. At this point, looks like I'll either have to live with it, pony up the $300 for a filter, or sell it and move on with something else.

Sounds like a ground loop hum. probably 60hz. Look at all your grounds and make sure they are all referenced to the same point. This includes you antenna or cable. Try disconnecting them one at a time to see it the hum goes away. If you have two different grounds of slightly different values it can set up a current which generates the hum. Plug into a dedicated power receptacle or get a power conditioner whick you plug all of your equipment into so a common ground is guaranteed.

More than likely it is standing DC on the line rather that a ground loop but that is worth investigating.
I have been told that this can come from a number of different sources including your neighbors that are on the same transformer.
When my 7500 started to do the cyclic hum I thought it was from a new fridge that we bought so I unplugged it and nothing changed.
So I do not know where my problem actually came from.

I thought ground loop hum was audible through the speakers? I don't have that at all...it's just right from the amp. I've had the amp (and everything else) plugged into a Belkin surge protector, but I tried plugging the amp directly into the wall outlet and no change. The only connection I have with my satellite receiver to the preamp is via an optical connection. It's connected to the TV via HDMI. I guess I could try a 'cheater' plug on the amp to see if that's the cause. I'm leaning more toward it being he standing DC that's causing it at this point, as the hum/buzz is just at the amp.

og33 - PM sent.

Interesting development..had the amp on yesterday for about 4-5 hours playing mostly 2 channel music, but some multichannel too, and no hum/buzz at all. The amp was dead quiet. Guess I will see what it does over the weekend.