Can somebody tell me about the preceding tone I hear on the Motorola Radios used by Nashua Fire? I understand that when a user presses the PTT button a 3 beep tone it emitted by THEIR radio as part of the trunked system letting the user know that the system has recognized the radio, processed the request to transmit and that it is okay for the user to talk. However, what is the single tone sounded out of the OTHER radios preceding the communication when one radio keys up the microphone. I notice this sound is only heard on the fire department radios and not by any of the other radios in the system, such as those used by police. I think it is a useful feature of the radios as it lets the firefighters know to begin listening to a transmission, but I am not sure if this has to do with it being a trunked system or if it is a feature of the Motorola Radios they are using.