A couple of work-arounds for the HX One raising your overall noise floor (for me it was a lot of hiss, but if there's any other noise in your signal chain it'll make that more apparent, too) are to set it to True Bypass - so that it's out of the signal chain when it's off - or using the noise gate.
Otherwise - as others have mentioned - having the HX One in your signal path before drive pedals really makes for a LOT of added noise. That was really problematic for me.
Disclaimer: When I asked about this issue elsewhere, I had some people telling me their units were dead silent. I don't know if I should attribute that to everyone's hearing being different or manufacturing tolerances. I just know that in my case I was running an otherwise very noise-free setup (CIOKS DC7 power supply into a Fuhrman AC-215 power conditioner) and the HX One was the only thing adding noticeable noise to my rig).
