Train (sound)
A train is a sound that was registered and recorded on March 5, 1997 by hydrophones in the Pacific Ocean . The cause of this noise and the exact location of its origin are still unknown.
So far, the noise has only been registered once by the National Oceanic and Atmospheric Administration with the help of the US Navy's Equatorial Pacific Ocean autonomous hydrophone array . NOAA suspects the noise was caused by a large iceberg colliding with the ocean floor.