I have a new HX/DA 30 watt combo. Couple questions.
When you first turn the power on (standby remains off), do you hear the hum from the amp? ie. you clearly know that the amp is on from a foot or two away. (I don't think any of my other amps, which are arguably modern style, make this noise. About all you hear is a fan if there is one.)
When the amp is up at a decent volume, and your guitar volume is up with ALL strings muted, do you hear a bit of 60 cycle hum and/or hiss? If I switch to a single-coil, it's quite hummy, and if I switch back to HBs, the hum dramatically drops, but it's not zero. Interestingly enough, when I turn the guitar volume all the way to zero, the minor hum goes away. I would think that if the amp was the source of the hum, turning the guitar volume off wouldn't cure it, unless of course the guitar volume is grounding all the stuff in the amp.
I'm still trying different outlets and / or cables. I like in an old house, but the wiring had been completely re-done 10 years ago. Could be that different outlets were done at different times. I have a Furman power strip for my rack, but I'm not sure if that would "correct" a bad outlet.