I hope that's not the case, but I certainly will return the 7000ES if they don't have a fix. Attached is my hum - was your similar to this? I had to 'click' an onscreen menu to get it to start as it only plays with detected AV content, once it stops detecting AV content it stops generating the hum after about 10 seconds (which would be a good indication its not a ground loop hum and is generated by the unit)
Dropbox Link (you can play file in browser without download): https://www.dropbox.com/transfer/AAAAAMzmO4deQoLFjJ6ziP6UUOPkFDOALGmMGGzbz6u1XmD9qaqoW30
Granted I am next to speaker to capture the hum so it seems much louder than it is, but a discerning ear can easily hear it.
This was my hiss on both units (this recording is with 360ssm on) https://voca.ro/1ZPGl7ibEA9B