audiopollution

Hello - Did you ever find any answer to the intermittent humming sound you are/were hearing ? I am from the SW U.S.A. and hear the exact same sound in my home. There seems to be no recourse other than masking noises to assist in sleeping. I am an engineer, and I can tell this is a man-made sound propagating from the vicinity. All of my utilities are buried, so I suspect it is something to do with them....