The Bloop is a famous oceanic fart detected by the U.S. National Oceanic and Atmospheric Administration in 1997. The sound was picked up on SOSUS - a Cold War relic, originally designed to track Russian submarines. Although the Bloop's acoustic signature makes it look biological in origin, it is much much louder than anything previously recorded and dwarfs sound by even the largest whales. The Bloop is a favorite among cryptozoologists, who think it demonstrates the existence of some type of cryptid or alien.
SOSUS has picked up other unusual sounds, which have been labeled "Train", "Whistle", "Slowdown", "Upsweep" and "Gregorian Chant." Of these, Bloop and Slowdown remain unidentified.