N4IN asked about: "...then gradually a hum will start in on the audio...(etc.)" Is it 60 Hz or 120 Hz or something else? If power feeding the rig is pure DC, then how do you account for 'hum'? Something oscillating within, or maybe hum being picked up from an external source such as a power transformer too near to the rig? Please describe. 73, Roy K6XK