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.
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.
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.
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.
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.
In January, something both amazing and frustrating at the same time happened in the field of UFO studies. Approximately 130,000 pages of files from the 22-year Air Force UFO study -- Project Blue Book -- were finally made available to the public for free online. Ever since Project Blue Book ended in 1969, anyone wanting to research those files prior to 2015, had to pour through microfilm files at the National Archives in Washington, D.C. Writer and producer John Greenewald, creator of The Black Vault -- a huge online compilation of government documents -- converted Blue Book files from jpeg images into searchable PDF files. It was every UFO researcher's dream come true. But it didn't last long. Shortly after the files became available, they were removed from The Black Vault by a company called Fold3, which posts military files, claiming to have a copyright on the old Air Force files. Easy come, easy go with the UFO files, it seems. But there's still hope that those files will once again see the light of day. This image is a re-enactment of one of the most credible Project Blue Book cases, from 1964, in which Police Officer Lonnie Zamora witnessed an egg-shaped craft along with two beings in Socorro, New Mexico.
In February, a television production crew in Lima, Peru, videotaped a purple-colored disc-shaped UFO hovering in the sky near a construction site. Eyewitnesses reported seeing the object for up to two hours. Initial possible explanations included a drone or a kite.
At the end of April, San Diego's NBC News affiliate captured an unusual colorful grouping of lights over San Ysidro, near the U.S.-Mexico border. The red, blue and green lights were flashing and changing colors. When HuffPost contacted the TV station, a reporter said she was instructed by station management not to give out any information about the incident.
In April, a new update was released about a couple of photos from 2013 showing a disc-shaped object over a copper mine in northern Chile. Witnesses said they watched the object for over an hour as it moved around and hovered. Investigators for CEFAA -- Chile's official government UFO study group -- examined the photos, and ruled out experimental aircraft, planes, weather balloons or drones. The study concluded "It is an object or phenomenon of great interest, and it can be qualified as a UFO."
It took several updates to this story to try and figure out what exactly it was that a family, vacationing at Scotland's Loch Ness captured in a photograph above the 22-mile-long lake in April. Their camera seemed to catch a pair of objects (see image with close-up insert) moving in the sky over the lake. The controversy heated up when Metabunk.org stepped in, claiming that the family had merely photographed a dual reflection of a room lamp. To this day, both parties believe they are correct: the family insists it was no lamp reflection and Metabunk maintains it was.
On July 4, Tom Sanger videotaped a colorful display of changing lights over the Sabino Canyon, northeast of Tucson, Arizona. In late August, an updated report by OpenMinds.TV suggested these lights were caused by "human activity" at a mountain lookout point, i.e. the headlights of oncoming vehicles.
Two separate cases of unusual-looking lights over different continents within a few days of each other prompted speculation from alien life to Chinese lanterns. The image shows objects over Osaka, Japan (at left around the end of July) and Milwaukee, Wisconsin (on July 25). The Milwaukee objects were later identified as an Army parachute team, performing during the city's annual German Fest. Still no official word on those Osaka lights.
It wasn't exactly of the same legendary caliber as the 1947 Roswell, New Mexico, incident, but it was unique in its own way. On Oct. 17, police in Kingston, London, sent an emergency response team to a location to check on an unknown object that was on fire. When officials arrived on the scene, they thought, at first, they were looking at a crashed UFO! The orange-blue hemispherical object was partially smashed with pieces of it strewn all around. Turns out, online detectives helped determine the UFO was, in fact, a pizza oven that may have fallen off a truck. That's some pizza delivery service.
When International Space Station astronaut Scott Kelly snapped a photo of south India on Nov. 15, Internet UFO hunters speculated about the bright, tube-like object at the upper right of the image. It was just the latest in a long series of objects photographed by space station astronauts that fuel Internet chatter about UFOs. In this case, however, a simple adjustment of brightness and contrast of the original image clearly reveals that the UFO in question is a UHF antenna attached to the space station.
Many people saw and videotaped a spectacular bright object over several cities in Siberia on the night of Nov. 17. Initial speculation included things like UFO, alien wormhole, and a secret Russian military rocket launch. Former NBC News space consultant James Oberg -- an expert on all American and Russian space activity -- confirmed that the bizarre spectacle was part of a Russian missile test program. While not an ET invasion, it doesn't lessen worries over increased tensions between Russia and members of NATO.