McCormack Power amp "buzz"

Hello all, I recently set up a system with NHT 2.5i speakers, a Peachtree Decco (used as dac/pre-amp), and McCormack DNA 0.5 deluxe as power amp.

The Decco can be used as dac/pre or as dac/integrated so when I hook up my speakers to only the Decco and turn it on, I get zero sound coming through the speakers. However, when I have it hooked up as I usually do - using the Decco as dac/pre going into the McCormack power amp - I get a "buzz" coming through the speakers when I turn the Decco and power amp on. This continues when music is playing, but is relatively quiet, so it can't really be heard unless you put an ear next to the speaker. Though it would be nice not to have it during very quiet passages. Any ideas what might be causing this?
Try lifting the ground on the Decco and the McCormack one at a time.
Hi all, so I finally picked up a couple of 3-2 cheater plugs to try and lift the grounds on the Decco and power amp. Sure enough, lifting the ground on the power amp solved the problem, the buzz is gone!

Any ideas what my next step would be? I don't want to leave the amp ungrounded permanently because I know the risks it may pose. Thanks a lot!
You could try one of the Jensen isolators between the preamp and amp.

I had a ground loop which was causing a VERY audible hum coming from my speakers when I had my McCormack DNA-1 Deluxe hooked up to my TLC-1 Deluxe preamp. Before that I had a Threshold 400A hooked up the the TLC-1 Deluxe and the hum was there as well. Both amps were plugged into the same outlet. I had a ground loop that I just couldn't isolate.

I ended up using an Ebtech Hum X Ground Loop Hum eliminator to remove the hum. It worked in my system. The hum was no longer audible. I know this isn't well regarded amongst the audiophiles here but it worked for me.

Ebtech Hum-X

Good luck.