Hi Top,
I've recently had a similar frustrating problem with my mic's. My GL2WAY CB would give a horrendous squeal when I pressed the TX (transmit) button that would over-ride anything I was saying. Heard it both on the bike's speaker system (bike or helmet, whichever was selected) and the receiving bike heard the squeal also.
Now here's the interesting part - my mic's would work on intercom. Press the TX button, could talk (had the squeal, but could talk). Release the TX, go to try it again and even though it transmitted a squeal, the mic's were dead. Thought the mic's had been blown. Switched helmets, connector harness, all the same crap you've done.
Also turned bike off and left alone. Came back later, mic's work. Okay, so it seems I've tracked it down to the GL2WAY.
Seems I get one use of the mic, then goes dead. Turn the audio system off, count to ten and turn back on, usually get the mic's back. Unplug the 2way, have my mic's, intercom is okay. Press the TX switch - no CB installed but just checking. Still have mic's. Swap my 2way with a buddies, try reconnecting all the various harness connectors, don't have an issue. WTF - bad 2way?? Got with Pete at BikeMP3 (Pedro66 on the board). Got some tips regarding additional ferrite filters. Eventually with re-routing wiring, filters and planetary alignment, swapping radios back and forth, got rid of the squeal and my mic's work. (Now have to work on getting a mild squeal out of my buddies system).
Long story to give you the background. Appears that for whatever reason there is some sort of loop feedback (non-tech term here) that shuts down the mic input until the charge bleeds off. Appears one of the things that helps is additional ferrite filters on the system, the other is make sure the connectors are fully inserted. Remove and re-insert if necessary. PM me if you have additional questions.