•it starts when I turn it on (w/ST-70)
•it gets louder as the tubes warmup
•is unaffected by the volume pot
With only a cd player hooked up and playing, I was able to get the hum to stop completely and get a clear signal (though only through one channel/speaker) by placing my hand across the other unused RCA's, the sides of the main out RCA plugs, and the chassis. (This was done with the cover on and secured with screws)
I've since read that it is standard practice to upgrade one component at a time to simplify troubleshooting. The odd thing in my circumstance, this hum sounds exactly like the hum it had in stock form.
Any suggestions are welcome and appreciated!