The hum that only a few can perceive: Potential sources of a low-frequency sound

Some people occasionally hear a low buzzing or humming sound that doesn't have a clear source. An estimated 2–4% of the world ...
Ars Technica

Case vibration noise: repeating low hum, like a huge fan at low speeds

Ok, you know the sound those GIANT fans make in movies, like the huge turbines in massive air vents, the blade goes by slowly making that "whoosh" sound that's a low frequency sound.<BR><BR>My ...