NC222/300/250 here with absolutely no hum.
Thank you all for confirming you did not have hum. It does not solve my issue though 
Luckily it’s not constant but sufficiently annoying I need to cut power to remove hum when working from home.
A 2k solution is not on the table for me. Maybe I will try a DC remover
funny I get a bit humb when 332/350s turns on and then it disappears. It may be my ansuz distributor performing part of it’s magic or the components themselves.
I get hum with my 222/300 and with my NAP 300 DR. Some days it’s really rather noisy and other days nothing at all. I’ve tried turning off other things in the house but there is no obvious culprit. The 222/300 goes quite in standby. How do I check for over voltage?
That’s normal. A very slight purr that dissipates after about a minute.
I’ve always had that and don’t even consider it to be a hum since it goes away so fast.