Sounds like feedback. Unplug other headsets and turn down any volume on any speakers . see if it persists.If gone, plug in another headset, again with its vol right down, see what happens, gradually turn up volume to see if and when the squeal returns. The fact it just happens on one headset maybe just a mic sensitivity setting on the headset (assuming it has one) or perhaps the sidetone level thru the comm getting back into the system.
When you say comm, assuming you mean normal VHF comms ?