The microphone is not supposed to be hot unless you want it to be hot. If you have the VOX turned way up so that the microphone is open (always hot), or you push the PTT switch, or you raise your voice to trigger the VOX. Those are the only ways the microphone should be hot. Once the microphone becomes hot the intercom becomes activated, once this happens any audio source you are listening to drops to a very low volume. This happens because the radio thinks you want to talk to the passenger and if the passenger is listening to say an FM radio station with the volume turned up (like me wife grooving down) then the passenger would not be able to hear you over the radio station.
If the microphone activates on a turn prompt it defeats the purpose. The radio will lower the volume of the turn prompt (as it would the FM radio station) and you may end up not being able to hear the turn prompt, that defeats the purpose of having the NIM automatically interupt the radio when a turn prompt is present. Activating the microphone thus activating the intercom is not the way it is supposed to work, if your microphone activates on a turn prompt your NIM is bad.
Jim