Came across this story on the LiveScience website:
Earth gives off a relentless hum of countless notes completely imperceptible to the human ear, like a giant, exceptionally quiet symphony, but the origin of this sound remains a mystery.
Now unexpected powerful tunes have been discovered in this hum.
Fascinating to think about, yes?
Here's a link to the column by Mark Morford (of the SF Chronicle) that brought me to the original story.