You probably need to unplug the mic from the unit, check what is coming out of the unit to where you have your phones plugged in. If that's clean of noise, re connect you mic and see how it sounds then. Also try various presets and the bypass on the unit to see if the hum alters, turn it off and check for hum with just the dead unit connected. Check the mic settings on the helicon, in the set up menu, as there is attenuation there for various mic output levels. Some of the heavy duty effects will apply those effects to room noise as well as vocals. It does take a while to get everything balanced to get optimal performance, it can be frustrating. It's a new piece of kit which you are finding your way around, like a lot of this kind of gear it requires faith and patience to get the best out of it. I suggest you use a dynamic mic to start with as condenser mics tend to be rather lively, also make sure the phantom is off unless required by a condenser mic. I have mine connected with two short 1/4 guitar leads to my mixer, no hum issues.
I may be having a few sherbets as the evening progresses, and may have to get back to this thread tomorrow if you require further suggestions. All the best.
Tim