I asked what could be causing a loud squeal in my headset when I key
the mike.

well I fixed it. it required absolutely no modification to my
altronics headset at all and there was no problem with the wiring or
the Icom A200 radio.

the problem was corrosion on the brass components that form the base
of the antenna wire and the antenna mount. I cleaned these up with a
wire brush and brasso to remove the oxide. I took the opportunity to
give the antenna a new coat of paint, screwed the now clean faces of
the antenna mount together and viola! no squeal anymore.

thanks for the suggestion by the poster in another thread. he was on
the money. corrosion in the antenna mount was the culprit.

Stealth pilot