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Stories about: humming

The Source of Earth's 'Hum' Finally Discovered Though our ears are too insensitive to perceive it, the planet is constantly generating a low-frequency humming noise, which was first discovered with instruments in 1998. At a frequency of around 10 millihertz, the sound is far outside our hearing range, as we can only perceive sounds as low as 20 hertz. Now, scient... 10 August 2009 03:06 GMT