Bose A20 problem

So I made the leap and bought an A20
Plugged in, linked to my phone, got some rock music on, and appreciating the ANR. Did run up, pulled to hold and keyed the mike... screeeeeeeeeeeech! Like a feedback but It didn?t change with mike covered or ear muffs held tight. Changed to rear seat jacks with same results. Went back to hangar read Bose instructions. Gave in and swapped out my Flightcoms and finished my flight.

Any ideas before I box them up for return?

Which mic/cable are you using: twin GA plugs or Lemo? Is the mono/stereo switch set the correct way?

-Marc

Try pulling the MIC plug (assuming you have duel GA plugs) and test again. If it still goes screeeeeeeeeeeech, you likely have a grounding issue in the PTT wiring, which is unlikely (it just closes a circuit to ground). If it doesn't happen, something is amiss in your MIC wiring, which is also likely ground related.

GA 2 plug. 2 other headsets work without a problem in front and rear jacks.

Update

Turned out to be mic gain and sidetone adjustments in the ICom. Works now.