I am currently waiting for our Part 145 facility to get back to us but maybe somebody of you has heard about this phenomenon:
2012 AS350B3e with a NAT AMS 43 TSO – ICS and as soon as the HORN switch engages, you hear a very high frequent tone in all headsets.
When you switch to pilot isolated, the pilot's headset goes quiet, everybody else still hears it.
This is also with headsets in the back (and/or copilot) unplugged.
When you disengage the HORN, it goes away immediately.
Switching to a Garmin GMA340H ICS could help
but is not the favoured solution for the problem at the moment
Any ideas? TIA