I have the same problem with the noise floor. Very noticeable hiss - never goes away - volume all the way down, phones down, XLR out's set to Line - or Mic - same results . . .
I am going into a very large and relatively new Yamaha Digital board in the main worship center- no one else has the issue, by process of elimination , it is the Helix. Shows up in the house, floor monitors, and our myMix IEM's.
The tech team folks and I are going round and round - I am about to the point where I can't use it in the worship service which is a deal breaker for me .
I had hoped the 1.0.6 software update would help - but no luck. I also have tried to use this as a USB Audio interface to my MAC for DAW use. Unsat.
Any ideas ? its more like white noise - not 60 hz AM hum mod .