Does the Earth hum? Scientists say it does. In 1998, researchers in Japan detected a mild, rumbling sound in the lithosphere even when there aren't any earthquakes detected. 

To test this yourself, try holding your ear close to the ground and listen- do you hear a sound that goes "thump, thump, thump?" If you can, seek medical help because something is very wrong with you. Either that or you were somewhere in Kenya with gazelles stampeding in the distance at the time you were doing the test.

That's because the earth's hum, although very real, is well below the hearing range of humans. Detectable only by the most sensitive seismometers, the hum is only about 10 millihertz in frequency.

The researchers who made the discovery hypothesized that the rumble may not actually coming from the earth itself, but from the force of air downdrafting on soil and pounding it to create the steady rhythm. However, American scientists recently concluded an elaborate research suggesting that the thump emanates from waves in the coastline hitting the shores and not from wind. Barbara Romanowicz, from the University of California at Berkeley, spearheaded the American research team and deployed seismometers worldwide to determine the source of the rumbling.

Meanwhile, Goran Ekstrom demonstrated in 2005 in Columbia University that the amplitude of the rumbling coincided and showed correlation to the energy picked up at coastlines worldwide. Now, Spahr Webb, a colleague of Eksrtom, says that he can demonstrate how exactly the ocean waves drive the humming. Webb says that when two waves of the same frequency travel at different directions, they alternately (the waves amplify and cancel each other out) create a pattern in which the surface of the sea becomes wavy, then flat, then wavy again. The motion creates a standing wave and ultimately, the thumps.

The waves then double in frequency, generating the humming of the earth from the seabed to the continents. That coincides with the Berkeley research which also noted that along coastlines, the hum signature is at its strongest, most notably in Vancouver right off the Canadian coast.

Webb also points out that Mars may have a hum similar to Earth's but, due to the absence of oceans in the red planet, the hum is most probably caused by "Marsquakes."