Speaking of issues with fans, I recently had a GR-300 repeater that started emitting a howling sound when users transmitted. Thought it might be a temperature change issue until I got to the site and heard the same noise as soon as I opened the door. Turned out to be the fan in the rear housing somehow causing a microphonic condition in the transmit radio; I suspect a loose shield. The quick fix was to remove the fan from the radio housing and place it directly behind the housing. No more noise, still supplying air to cool the heat sink.
Sometimes the little stuff can be very frustrating. Milt N3LTQ
