Hi... I'm facing the same problem... whether running on the laptop's battery or DC/DC power supply, and everything grounded to one spot... the humming noise seems to be there to stay... There's also a loud Whine which eventually causes feedback noise when accelerating while the volume is the up.
I've tried a Ground loop isolator from Straight-in but it blocked all audio to my connects2 interface... so it was worse the remedy than the disease...
Hope someone may finally show up with some kind of solution for this Issue, I'm starting to lose my never