More readers' thoughts for a homeowner investigating a humming noise.
Wayne Collins: "It is called 'sympathetic vibration.' Some part of the house, perhaps the A/C ductwork, a wall, or window, has a natural frequency that matches an energy source some distance . . . away. There may be a factory, generating station, or pumping station that runs all the time. Something in the house is vibrating in sympathy with that machine. It has a resonant frequency that is equal to, or a harmonic of, that machine.
Perhaps, by going around the house with a stethoscope, and by pressing on the air ducts, windows, walls, you can find the 'speaker.' Then, by adding some dead rubber or a stiffener of some sort, you can eliminate the hum."
Thomas Burgun: "I had that once. It was my sump pump, with a bad float switch happily burning itself up."
Lee Galiato: "I can't help wondering if the homeowner has a 'solar-powered' attic fan with 'battery backup' . . . on the roof or under a gable on one side of the house, which could explain . . . the humming even after tripping the main breaker."
Hank Graham: "Some septic systems have built-in aerators that are basically small propellers that stir the wastewater in the tank. Get a stethoscope and listen through the walls, floors, and ceilings to at least try to isolate the source."
Mark Schuller: "My house has a mushroom- style vent that would hum when the wind would hit a certain air speed and direction. A friend secured it . . . and applied a lubricant to cut down on the noise."
Douglas Parent: "About 10 years ago, we started experiencing a 'hum' . . . on windy days. I discovered it was the aluminum downspouts from our gutters. The installer secured the downspouts with brackets screwed into the house at the top and bottom of the vertical runs. The middle of the downspouts were vibrating when the wind would blow at a certain speed."
The homeowner will test these theories.