The 8180 installed in Car 1 at Dighton Fire every once in a while has a hum when it transmits. The Chief has told me that he notices it when his cruiser sits idle and when he goes to transmit dispatch advises him that he has a loud hum, I heard it the other day when he went to clear a call. I am almost positive that whom ever wired it wired it to a keyed outlet and not directly to the battery. Reason is is when he cleared the scene the other day he noticed his volt gauge was low and the hum cleared when the voltage was up? I looked at the specs and it requires 13.0 amps to transmit.