Bloop
"Bloop" is the name given to an ultra-low frequency underwater sound detected by the National Oceanic and Atmospheric Administration (NOAA) in 1997. The sound was recorded by hydrophones, which are underwater microphones, and it was notable for its unique characteristics and immense volume.
Scientists initially speculated that the sound could be produced by a large marine animal or geological activity. However, further analysis suggested that it likely originated from the cracking of ice in the Antarctic region, making it a natural phenomenon rather than a biological one.