Here’s a fix for a Line 6 Helix related ground loop problem I did for a customer a couple of years ago. He used the HX floor unit to control the amp channel switching and it created a really bad ground loop hum. It appears that the HX amp control sleeve is ground referenced, which is a pity on such an amazing unit.
You could modify a TRS cable to break the ground loop and it would work fine. On bigger stages though so the better is to build an adapter box to break the connection so that any length TRS cable can be used.
This isn’t a particularly common problem for Helix users, but it’s a real one that people occasionally come across.
The ground loop is caused by both pieces of gear. There’s a ground path running through the audio path of the amp and helix and a ground path running through the switching path of the amp and helix.
In some amps, the ground scheme will be such that noise is induced into sensitive parts of the audio path. The guitar amp designers won’t have paid much attention to this because most guitar amps with these sockets were designed before the advent of systems that share audio and switching functions, like Helix or GigRig. The amp designers were only expecting the user to plug in a latching footswitch to the jack. Latching footswitches don’t share an audio ground so no loop is created, so the designers didn’t need to control the ground currents. Thus the amplitude of the induced noise is determined by the amp grounding scheme resulting in different amps exhibiting the problem at different levels. Hope that makes sense. 
It couldn’t happen if the Helix sleeve wasn’t grounded, it wouldn’t happen if the amp’s FX connector sleeve wasn’t grounded.
The opportunity to break the ground connection entirely is only available at the Helix or switcher end. Whilst an isolated footswitch design could be built in at the amp’s end, this would be awkward because it would require an industry standardised LV power source in switching systems to power a relay (or opto) in the amp. Worse, it would stop the footswitch socket working with the very common stand alone latching footswitches (which have no power). 
No manufacturer is ever going to choose to do that. However it’s very easy to create a relay driver at the Helix end so that the sleeve is isolated from the audio ground (much like the GigRig remote switch options).
The noise level is also proportional to the amount of external noise as this is the external noise source that’s then picked up by the GND loop. In my workshop there’s plenty of external noise sources, just like in lots of venues. Studios, should hopefully be much quieter.
Unfortunately an ISO hum silencer box can’t fix it because this needs to respond to DC changes – the transformers in an ISO hum silencer will block DC. You could use one of those in the audio path to fix the problem by a different route (break the loop in the audio instead of the switching), but then that potentially messes with the audio path, so it’s not the best solution.
Above is a picture of the box I built for my customer. Very simple to make if you’ve got a soldering iron and a step drill. You can build one up yourself from the picture, or if anyone ever wants one building I can make one up at my usual labour rate.
Here’s the BOM to make your own:
Hammond 1590A style box.
Switchcraft 12B stereo metal jack socket
Neutrik NMJ6HCS or NMJ3HF-S or similar stereo plastic bodied socket
2 wires!
Here’s a video showing how it works: