OK, a little "RF in the shack" getting into to mic audio.
My first step would be getting a .1 to .01uf cap across pin 4 and 5 at the mic input of the radio. Pin count is 1-8 decending on the 8p8c input jack and a simple adapter could be made with the cap inside. The mic is 600 ohm dynamic, by the way.
Next would be ferrites on the mic cable.
Of course, you could move the antenna farther from the shack... but that's work!
-Mike.