I am having the exact same thing with my Orange Rockerverb MKIII and my Brunetti Mercury.
The hiss and jitter noise is woeful. Disconnect the helix, completely, and it's bliss.
The Helix is definitely the source of the woes.
So I too am looking for a solution before I need to sell my helix.
p.s. Had issues with my Fractal AX8 in the same 4CM scenario. I have sold that. ARGHHHHHH!!!