From Wikipedia:
Bloop or The Bloop is a mysterious ultra-low and extremely powerful underwater frequency detected by the U.S. National Oceanic and Atmospheric
Administration (NOAA) in 1997. The source of the sound remains unknown.
The sound, traced to somewhere around 50° S 100° W (a remote point in the south Pacific Ocean west of the southern tip of South America), was detected several times by the Equatorial Pacific Ocean autonomous
hydrophone array. This system was developed as an autonomous array of hydrophones that could be deployed in any oceanographic region to monitor specific phenomena. It is primarily used to monitor undersea seismicity, ice noise, and marine mammal population and migration. This is a stand alone system designed and built by NOAA's Pacific Marine
Environmental Laboratory (PMEL) to augment the U.S. Navy SOund SUrveillance System (SOSUS), equipment originally designed to detect Soviet submarines.
TL;DR: The Bloop is a shit-pants sound coming from the bottom of
the fucking ocean. The sound went across the entire South Pacific and was picked up by
underwater recorders placed
pretty much all around the ocean. To make matters even creepier, it is louder than any underwater creature ever recorded. Multiple sounds were recorded around the same year which were dubbed Whistle, Train, Slow Down, Julia, and Upsweep.
And yet another thing that makes Bloop even fucking scarier is the fact that the sounds were at a special frequency that shows that these were in-fact made by living things at the very bottom of the ocean. And in the H.P. Lovecraft (the guy that wrote about things like Shoggoth, Cthuluhu, and others) books, it states that the place where Cthuluhu sleeps is located almost exactly where The Bloop was traced. What the unholy fuck. Not to mention Lovecraft died 60 years before these sounds were ever recorded.
I played The Bloop when my cat was
in the room and my cat went fucking apeshit. I'm not kidding.