Sounds to me like that particular amp is malfunctioning. May be due to shipping or something else, but today's amp designs certainly should not be humming on the master bus like that.

Send it back.

Contact them first, they may offer a warranty repair/replacement to you.


--Mac
_________________________
"Keep listening. Never become so self-important that you can't listen to other players. Live cleanly....Do right....You can improve as a player by improving as a person. It's a duty we owe to ourselves." --John Coltrane

"You don't know what you like, you like what you know. In order to know what you like, you have to know everything." --Branford Marsalis