radio noise

I have a radio question. Glasair 1TD with Icom radio, older headset.
When the engine is running and charging 14.5 volts the radio howls
when I transmit. Engine off, battery voltage, no noise. If I put
a small screwdriver in the small hole in the headset and turn it down
1/2 turn, no noise. If I then take the headset and plug it in my old
Cherokee, it won't transmit until I turn it back up.

Are all headsets this voltage sensetive? Or just older ones? Is
there a fix?

thanks

Ed