The Blue Marble, Visible Earth- NASA
The planet emanates a constant rumble far below the limits of human hearing. Discovered in 1998 this low level "hum" was thought to perhaps be caused by disturbances in the ocean or atmosphere. Scientists now suggest that the Earth’s hum is caused not by earthquakes or atmospheric turbulence, but by ocean waves colliding with the seafloor. It will be interesting to see if there are other factors that are also involved with the hum. (The idea of the Earth humming or singing is not so new to many spiritual traditions.) Here are some articles about the 'hum', earth 'singing', moon hums, and earth "hiss"!
Earth Hums, and It's "Loudest" in Europe, Americas- National Geographic News, Aug. 10, 2009
Earth hums, and it's along the Pacific coasts of North and Central America and the west coasts of Europe that are the main sources of the sound, a new study says.
Mark Morford's excellent April 2008 essay in SFGate on the Earth's hum:
How to sing like a planet
Scientists say the Earth is humming. Not just noise, but a deep, astonishing music. Can you hear it?
"This is the kind of thing we forget.
This is the kind of thing that, given all our distractions, our celeb obsessions and happy drugs and bothersome trifles like family and bills and war and health care and sex and love and porn and breathing and death, tends to fly under the radar of your overspanked consciousness, only to be later rediscovered and brought forth and placed directly in front of your eyeballs, at least for a moment, so you can look, really look, and go, oh my God, I had no idea.
The Earth is humming. Singing..." (Read more)
Rain of meteorites makes the moon hum, New Scientist, Aug. 2009
Then there's the Earth's magnetic field interacting with charged particles from the sun, producing a different low frequency "hiss". (Of course there will be increased solar storm activity after 2012, of all years.):
Earth's Magnetic Field Hisses Due to Distant "Chorus", National Geographic News, May 2009