It probably has a noisy transformer that needs to be replaced.
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A dedicated circuit is great but may not alleviate the ground loop. You will probably have to break the ground on the device causing the loop. The culprit is usually cable or satelite TV. It's odd that the hum didn't occur when you were only using the inexpensive surge protector. Did you connect all of your equipment to it?
My orig run of tv coax has been moved away from my 2 ch set up, however now my ST-2 antenna coax to my Magnum tuner runs behind my rack. AND there was a hum with a second cheap surge protector after all (I have 3 kicking about), a couple of days later. But I really had to listen for it (ear against the grills). Yes, all gear with the exception of one of two external power supplies was connected to the cheaper surge protector. I had run out of space/plugs. I followed the advice of many and turned off/unplugged system piece by piece until I was left with only the amps, and the hum. Another thing is even in my previous place of residence when there was a slight hum from my Bryston amp, I would flip the ground lift toogle and the hum would disappear. I experienced the same thing where I am now when I was using a 3BST, and the hum was from both the speakers, and not the amp transformer itself....madness.