Gorund switch doesn't change a thing (makes sense, since it only lifts the XLR's ground, as far as i know). Hearing it through HP out too. I took the board upstiars. Used a different power an guitar cable, different outlet and only headphones, still no difference. Even on my KRKs. No they are just straight in to the outlet. There are non of the mentioned utilities anywhere nearby. Disconnecting the USB doesn't change a thing either.
Just to make sure, if you have a highgain preset and touch the PRESET / STOMP knob, while letting go of your guitar strings, there is complete silence in your helix? I will open a support ticket now. Thx so far.