Now that you mention it, about 3-4 days ago while trying to go to sleep, I noticed a "droning" sound.  My first thought was to check the electric meter the next morning to see if one of those "Smart Meters" had been installed.  Indeed, it had been, so I attributed the sound to that.  However, last night the sound was not there.  It never entered my mind that it could be as you described in your letter.  Thank you for posting that.....I will be more aware the next time I hear it..

Maranatha!

Linda