My brother in law and I were tuning a new antenna for his Cobra 18 WX
ST and when we got the SWR as low as we could, tried it out. As he got
further away during a test run I encouraged him to speak up because he
wasn't getting decent modulation. When he did the result was pulsating
oscillations that obscured his audio.

I'm an audio guy, but I mix rock concerts. The type of squealing I
usually deal with is some jerk guitar player wanting 130 dB SPL from
his monitor wedges. There's not any possibility for audio feedback in
this case, my rig was two miles away from his and he doesn't have
talkback.

At any rate, the question is, would replacing the audio amp chip do the
trick, is the part readily available, and is it anything a guy with
plenty of soldering experience couldn't tackle.

Thanks in advance...
Jon