Riddle Me This Batman; Low Frequency Hum: SOLVED

constant or it comes and goes? in the right weather conditions our rooftop TV antenna will vibrate and sound like a hum. but it has to be the right combination of temp, humidity, barometric pressure and wind.

or

if you live near a high powered VHF radio transmitter like at a major airport the radio modulation can cause metal pipes to vibrate and hum. rare but it can happen.