Second that, my Zulu manual says to leave the switch as-is and call the company for more information. I have not tried moving the switch. For most of the GA airplanes I get into, I will have to adjust the squelch on the audio panel because sometimes it will be set too sensitive and the mic will stay open. I have had a few instances where the headset squealed/hissed while talking on the radio, but I think that was an audio panel problem.