Why do bees hum? Because they don't know the words ! But it looks like the planet earth might hum as well - at frequency of around 2 to 7 milihertz - way beneath the threshold of human hearing. And until now, scientists were baffled as to how this noise was produced. Most intriguingly, the noise seems to come from the oceans and not the land. According to two scientists from California, Junkee Rhie and Barbara Romanowicz, the hum is the result of storm energy in the pacific and southern oceans being converted into infragravity waves - very spaceage sounding. Powerful sea waves generate these infragravity waves during storms, and some of the wave energy gets converted to seismic waves on the seafloor. It is these seismic waves that make the noise, by an interaction between the atmosphere, ocean and sea floor. The team measured seismic energy emitted by the earth, and found that the hum mainly comes from the seas during the most stormy seasons, confirming their ideas. Scarily, this energy is the equivalent of an earthquake measuring about 6 on the Richter scale being released every day !