I did a service call last year, same complaint, hum/buzzing in the house.
After two hours, traced it to the master bedroom 4 poster bed. Listening with a stethoscope, we found an expensive Bulova watch, which uses a tuning fork to keep accurate time, against the head board. The tuning fork in the watch was vibrating the bed, like a piano when a key is struck.
Put the watch in a sock: no more hum.
Got a nice Yelp write up for that one:
6/18/2013
For the past six weeks, we have had a bothersome consistent low hum - which sounded like a transformer going bad in our bedroom - in the wall right behind the headboard of our bed. It was a low hum that, at first, you might not notice. BUT at night it was so noticeable that I could not sleep in our bedroom.
We unplugged everything in our bedroom and took out the LED lights we'd recently put in but still, the hum. We had our contractor come out twice, his electrician came out, too. They checked the attic. They turned off the central breaker to the house and still we had this hum. They could not figure it out. We had a friend that's an electrician/handyman come out - just because he was curious - and he couldn't figure it out. We talked to the solar panel folks, we talked to the folks that put in our whole house audio system. We had our two brilliant neighbors (astro physicist and computer genius) come over and they sat around for 45 minutes, conjecturing that somehow it was coming from outside and resonating in the wall. We had the pest control folks come out.
I was ready to rip out the wall to find this problem. Someone suggested Andy Cook of Cook Electric. I called him last week, explained the situation and was surprised that he was able to come early Monday morning. Andy arrived with two very nice respectful young men. They were super aware of putting on shoe covers to keep the house clean and they went to work. Andy had a stethoscope and some sort of sound detection device. They heard the noise and began to try and identify WHERE it was coming from. They pulled the bed out. They listened to the wall, they went down to the kitchen where they could hear it, too. They turned off the electricity and they could still hear it. This went on for a full hour.
Finally, one of the young men put the stethoscope on the bed and swore that it was IN THE BED. They immediately lifted this massive bed up and slid towels under the base. The sound was IN the bed. Andy immediately began to look under the mattresses, pillows, etc, and he found ....... my husband's 1960 Bulova Accutron Spaceview watch that had dropped down between the mattress and the headboard. It has a tuning fork that hums at 360 hertz. It was pressing against the headboard which amplified the sound!
I'm so happy to be sleeping in my own bed again! Thanks to Andy and his awesome team!