So this might not apply as I had something similar on my helix(but not HX effects) - do you have any pedals selected as stereo versions but everything is mono as far as inputs and outputs? Had an issue where I selected a stereo tubescreamer(not the real name, obviously >.>) instead of mono on accident once and it caused everything to pan L/R and sum back and basically sounded like a constant modulation/oscillation effect. It's like a ping-pong delay with a super short delay time, but you hear it and it drives you crazy lol.
Might not be your issue, but also might help someone else if they've done the same thing.
