that is a post from 2009.thats 13 years ago
Necrothread. But I figured out why this happens with ham rigs in the years that have passed. If the radio wasn't golden screwdriver'd , then the problem is usually caused by a microphone / audio chain input that has the phase 180 degrees in reverse of what it should be. There are a number of things that can introduce this phenomenon including impedance mismatches, cabling, adapters, etc. One way to solve the problem is by using something like the W2IHY iPlus, which is really an audio switch to allow you to use one mic / speaker combo with up to 3 rigs. But it also contains a phase switch which will change the audio output of the device by 180 degrees to solve this.
In my older post about the Icom 746 Pro doing the same thing, I later added the W2IHY audio stack, tried the audio phase switch and the problem was solved. I also experienced this on AM with a few other rigs since then.