Joe Hull wrote:

...  However, remember it is only when the engine is running – and also remember that in a Cozy that bad boy is 8 feet from the instrument panel.  So, since it’s only there when the mic is keyed it has to be something that gets energized on the PTT ground wire or on Mic cable only when the engine is going.

   Ah, and what else is running when the engine is?  Alternator, for one.  Does the noise
fall off proportional to engine speed, if you kill the engine while transmitting?

Dale R.
COZY MkIV #1254