From secret Russian signals, to bizarre marine soundtracks, to sonic booms and intriguing interference, our world is plagued by unexplained soundscapes.
As this video reveals, above, scientists continue to be perplexed about paranormal phenomena observed many decades ago.
Here are the 10 mysterious and unexplained sounds...
10. Secret Russian Signal
Broadcasting at 4625Mhz, a strange, repeating radio signal has been observed emanating from broadcast stations in Russia.
While the signal was first believed to be broadcast from a station in Moscow, the signal has since moved towards St Petersberg.
This has led to speculation it is a means of communicating secret messages to members of the Russian military.
9. Colossi Of Memnon
The giant statues at the Theban necropolis, west of the Nile, are believed to omit a bizarre sound - following a devastating collapse in 27 BC.
The weird noise can be heard around the break of dawn and is described as being similar to an instrument's string breaking.
Scientists have debated its cause - with dew surrounding deep cracks within the stone thought to offer a potential explanation.
8. Quackers
Strange noises emanating from deep below the Arctic Circle were observed by Soviet submarines during the Cold War.
The sound is said to have resembled the croaks of a frog, with crews convinced they came from a biological source.
7. Bloop
An extremely low, but highly powerful frequency was picked up by researchers over several months in 1997.
Investigations led scientists to a potential origin of the sound close to South America, yet its true cause remains unclear.
6. The loneliest whale
Also known as the 52-hertz whale, this high-pitched, short sound is "unlike any other on Earth".
Marine biologists are baffled as to its origin, with a possible mutation or deformity speculated to be a possible cause.
Dubbed the loneliest whale, the animal is unlikely to be able to communicate with any members of its own species.
5. Slowdown
Yet another marine mystery comes from a sound emanating from deep within the Equatorial Pacific Ocean was discovered by the US Oceanic Administration.
The frequency slows down gradually over a period of seven minutes, earning it the moniker 'Slowdown'.
4. Taos Hum
The town of Taos, New Mexico is plagued by a strange, low-frequency hum, reports suggest.
Intriguingly, it affects around 2% of the population wherever it is observed - within their bodies rather than outside.
3. The Upsweep
First detected in 1991, this car alarm-like sound is said to oscillate between frequencies becoming increasingly higher pitched.
Observed by US scientists, the level of sound was such that it could be detected throughout the Pacific Ocean, peaking in spring and autumn.
2. Skyquake
This unexplained boom-like sound is common to many waterfront communities.
Described as very loud, distinct thunderclap scientists continue to search for its origin - which could be the sound of caves collapsing underwater.
1. WOW signal
A search for extra terrestrial intelligence uncovered a narrowband radio signal lasting just 72 seconds, and recording as being 30 times louder than the sound of deep space.
With this potential clue in mind, astronomers have worked hard to identify its origin - but have thus far failed to do so.
Suggestions continue that the sound represented potential alien contact with Earth.
