In 1997, scientists detected a strange sound unlike anything they'd heard before in 1997 - but years later they managed to figure out the culprit.
Some people believed the mysterious ocean sound - dubbed 'the bloop - was from an unknown creature.
But years later, the NOAA deployed hydrophones to study seafloor volcanoes and earthquakes.
They found it came from an icequake, or an iceberg breaking off an Antarctic glacier.
NOAA seismologist Robert Dziak told Wired that the frequency and duration were similar to other icequake signals they'd recorded off Antarctica.
Watch the video above to listen to the sound.
More and more of them are happening because of global warming.