Just an update. Hum came back. The transformer did not fix it. Basically replaced every part - still not working.
Finally replaced the control panel - got it off ********, NOS, as the unit has been discontinued for some time. There are companies that will repair the circuit board, but I did score one.
This seems to have fixed the problem. Apparently the relay on the circuit board was bad/wore out over the years
Been working great for the past few weeks, so I am 99% sure it is fixed.