eurocopter usual have "simulcom" which reduces the sensitivity of the rx side of the none transmitting radio..
I would check the ground planes of the aerials.
if one is on the cabin roof as its composite there is a copper tape which forms the ground plain it can corrode/split.
is the feed back in comm 1 when you transmit? does the radio actually tx and whats the quality like?
is it a problem with your sidetone?