Mysterious Sounds From The Depths Of The Sea To The Sky Overhead

You can see and hear Caitlin Schneider's full list of unexplained sounds over at Mental Floss. 

Sometimes unexplained sounds have a perfectly logical scientific explanation, other times, no matter how logical the explanation may be, you still don't believe it. The following sounds are unexplained, but there are theories about their origin. We invite you to speculate wildly.

Credit PMEL Accoustics Program / NOAA | pmel.noaa.gov/acoustics/sounds/upsweep.html

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NOAA | pmel.noaa.gov/acoustics/sounds/upsweep.html

Upsweep has been around since 1991, and according to NOAA the origin of the sound is unresolved. The most likely explanation for the sound offered thus far is that it's the result of underwater volcanic activity. According to researchers there isn't enough variation in the sound's tone for it to come from something biological. 

Related: Meet the Bloop

Every sensor in the equatorial Pacific autonomous hydrophone array picked up the short 15 second sound known as "Julia". Translation:  it was super LOUD. Scientists haven't confirmed the origin of the sound which was recorded one time in March of 1999, but they think it was likely an iceberg running aground. We're not buying that, it definitely sounds like a giant sea monster.

Related: NOAA's PMEL Acousitics Program

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Also known as the "52 Hertz Whale" scientists believe this sound is a call from a lonely whale because teh sound it makes registers much higher than any other whale they've heard. A group of filmmakers--including Entourage star Adrien Grenier--recently launched a successful Kickstarter campaign in order to find this mysterious whale. 

This is a really weird one. The Hum has been recorded all over the world, but not everyone can actually hear the noise. The people who can hear it have a lot of theories on its origin and many speculate it has to do with HAARP. The problem with low-frequency sounds is that people often feel the sound rattling in their chest, it makes it seem that much more mysterious and disturbing. If you're the kind of person that can hear a noise like that and not be bothered by the fact that you don't know the origin, it's likely you'll accept the scientific community's assessment that it could be any number of things. 

Related: Tropicana Field Is Haunted By G-G-G-G-Ghoooooosts