Having the same problem. Tried the suggestions listed but having a flange like sound when on channel 2 of rectoverb. If I turn down the effects loop on amp, the amplifier sounds find but not effects coming through. That makes sense, but the more increase the amps effects loop, and the more helix coming through it sounds like a flanger. If I turn down the helix's volume knob, again the channel 2 sounds great but no helix sound. I'm sure it's something with the send returns, but can't figure it out.
