I had that same problem a couple of months ago. Change/Turn off Mod Note MIDI Channel?
On channel 2, the mod note is played, the beta patch note Mono V2 beta patch note - #13 by Mathieu says you can change it like this: Go to Midi param with [FUNC] + [MIDI/Clock], hold [MIDI/Clock] and select channel with a [SEQ] key
On channel 3, the “basic patch sound” is played by default. I couldn’t find a fix for that.
In the end, I just blocked channel 2+3 in my “MIO XL” MIDI hub for all outgoing traffic to the Norand Mono. You could also do this with the “MIDI Solutions Eventprocessor”, but maybe there is another solution?