Unplug all the inputs and see if it still hums. If not, you might be hearing a humming phono input or cables that are picking up electromagnetic noise.
Sure sounds like a transformer buzzing☹️. Bummer, I would pass. But that model is such a tremendous amp… I really recommend finding another. That is the kind of product that can change your audio life and every purchase in the future… in a good way.
For what it's worth. I have a halogen light set up on top of my TT with two settings. One medium light, the other one full bright. Bottom line is set on medium light I get a buzz from my amp but when switched to full bright, the buzz completely disappears. Don't ask me why, that's just how it is.
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