“The Bloop” is a mysterious, ultra-low-frequency underwater sound recorded by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997. For years, scientists debated its origin, with theories ranging from giant sea creatures to military operations, but it was later determined that the sound came from icequakes, or the cracking and breaking away of icebergs from glaciers, according to NOAA.

That’s what they want you to believe.