Out of interest, David, have you taken it out of the setup to test the reverse ? I always find this a valid check to confirm that the effect is consistent. IIRC the ID41 was designed to better protect for such interference vs the ID40. I tried and still have the little GISO unit from a few years ago, but, never really heard any difference.

That you hear something with this device into an ID41 is interesting.

Rgds,
Nick