Residents in Alabama were left baffled last week when a loud boom resounded across much of the state.
The boom, nicknamed 'Bama Boom', has left experts stumped, with suggested causes ranging from supersonic aircrafts to meteors exploding in the atmosphere.
This isn't the first time that the mysterious sound has been heard, and incidents are becoming more frequent according to some reports.
This year alone, similar noises have been reported 64 times this year, in locations including Michigan, Lapland, St Ives, Swansea and Yorkshire.
Scroll down for a full list of booms in 2017
Mysterious booms have been reported 64 times this year, in locations including Michigan, Lapland, St Ives, Swansea, and Yorkshire. Incidents are becoming more frequent according to some reports.WHAT COULD THEY BE?
In 2017 alone, 64 booms have been heard worldwide.
The cause of most of the booms remains a mystery, although several explanations have been suggested.
1) Sonic booms
A sonic boom is a sound associated with the shock waves created by an object traveling through the air faster than the speed of sound – such as supersonic aircrafts.
Sonic booms generate significant amounts of sound energy, sounding like an explosion to the human ear.
2) Military exercises
Many unexplained loud noises can be put down to military training, either at Army or Naval bases or in remote areas used for such exercises.
3) Controlled explosions
A controlled explosion is a method for detonating or disabling a suspected explosive device, such as bags left at train stations.
4) Unusual weather
Many loud noises link back to unusual weather events, such as electrical storms or thunderstorms.
Large meteors passing above Earth often produce shock waves that can be heard as a sonic boom.
6) Sound amplified from aircraft
Some have suggested that the sound was due to inversion - a phenomenon that occurs when a layer of warm air sits over a layer of cooler air, magnifying the sound of an aircraft miles away.
Some conspiracy theorists claim that the mysterious booms are noises created by aliens - although there is no evidence to support this.
Alabama, November 14
Cause: Unknown, suggested explanations include a sonic boom from an aircraft or a meteorite
The Birmingham National Weather Service tweeted: 'Loud boom heard: we do not see anything indicating large fire/smoke on radar or satellite; nothing on USGS indicating an earthquake.'
The service suggested that the sound was either caused by a sonic boom from aircraft or a meteorite from the Leonid shower.
But Nasa has since cast doubt on these explanations.
Speaking to ABC 3340, Bill Cooke, head of Nasa's Meteoroid Environment Office, said that the boom could have been caused by a supersonic aircraft, a ground explosion, or a bolide - a large meteor that explodes in the atmosphere unrelated to the Leonid shower.
While the noise was picked up by the US Geological Survey, data suggests that the boom wasn't the result of an earthquake.
The boom may have been caused by a military flight by a supersonic jet, although the US Air Force is yet to confirm this.
The Bama Boom is just one of many mysterious booms heard worldwide this year.
Idaho, November 15
The day after the boom in Alabama, a similar noise was heard in Idaho.
Multiple people reported hearing a loud boom over the Lewiston-Clarkston Valley around 23:00.
Many of the reports described the sound as being similar to a sonic boom, although its cause and location remain unclear.
Cairns, October 10
Cause: Unknown, suggested explanations include a meteorite, a gas bottle explosion or military plane
On October 10, a boom was heart over Cairns, Queensland that had the city baffled.
While the noise in Alabama was picked up by the US Geological Survey (graph pictured), data suggest that the boom wasn't the result of an earthquake
Residents' theories ranged from a meteorite to a gas bottle explosion or military plane.
An FA-18 Hornet plane was heard flying over Cairns the previous night, but no jets were flying on the night when the 'explosion' happened.
The Birmingham National Weather Service tweeted: 'Loud boom heard: we do not see anything indicating large fire/smoke on radar or satellite; nothing on USGS indicating an earthquake'
Abergavenny, May 11
Residents in Abergavenny, Wales, were also shocked after they heard a series of booms on May 11.
James Spann, AMS Certified Broadcast Meteorologist tweeted that no explanation had been provided by USGS, NOAA or EMA
Speaking to the Abergavenny Chronicle, one resident said: 'It nearly gave me a heart attack it was that loud. At first, I thought it was a shotgun blast or a firework, but it was way too loud for that. It sounded more like a tank going off.
'My husband said it was probably mini meteors colliding with the earth, but have you ever heard such nonsense?'
Again, the source of the Welsh booms has remained unsolved.
But other booms this year have had explanations behind them.
Other booms have been known to be caused by secret military missions. On May 7, a boom rattled Central Florida, caused by a military mission ending at the Kennedy Space Centre (stock image)
Lapland, November 17
Cause: Falling Meteor
On November 17, a boom in Lapland was caused by a fireball from a falling meteor.
Footage showed a bright light in the sky over Inari in Finland - but the flash was so intense it was also seen in Russia's Kola Peninsula and in northern Norway.
Stargazers reported seeing the sky 'light up like day' for a few seconds alongside a loud noise as the space rock plummeted towards Earth.
Eyre Peninsula, October 27
Cause: Falling Meteor
On October 27, another boom was heard over Eyre Peninsula in Australia, as a bright blue meteor shot across the sky.
On November 17, a boom in Lapland was caused by a fireball from a falling meteor. Footage showed a bright light in the sky over Inari in Finland - but the flash was so intense it was also seen in Russia's Kola Peninsula and in northern Norway
The loud bangs weren't caused by the fireball hitting Earth, and instead were caused by the change in pressure as the meteor soared through the air.
Speaking to News.com.au, Renee Sayers, a spokeswoman from the Desert Fireball Network, explained: 'The shock wasn't from it hitting the ground; It is like a sonic boom shock, a pressure shock.'
Central Florida, May 7
Cause: Supersonic flight testing
Other booms have been known to be caused by secret military missions.
On May 7, a boom rattled Central Florida, caused by a military mission ending at the Kennedy Space Centre.
The US Air Force tweeted: 'The Air Force #X37B #OTV4 has returned from orbit and landed safely at @NASAKennedy.'MYSTERY BOOMS IN 2017
|November 18 - Michigan|
|November 19 - Damascus - caused by airstrikes|
|November 17 - Lapland - caused by meteor|
|November 15 - Idaho|
|November 14 - Alabama|
|November 8 - Tennessee|
|November 4 - Oregon|
|November 3 - Minnesota|
|November 1 and 2 - New Jersey and San Diego|
|October 27 - Eyre Peninsula - caused by meteor|
|October 25 - New Jersey|
|October 20 - British Columbia|
|October 17 - North Carolina|
|October 10 - Detroit|
|September 25 - St Ives|
|September 22 - Temple Terrace, Florida|
|September 17 - Maryland, Pennsylvania, New York, Virginia, Delaware, New Jersey, Ohio and Massachusetts - caused by meteor|
|September 7 - Moranbah, Australia|
|May 30 - Tauranga, New Zealand|
|May 26 - Kent|
|May 24 - Texas|
|May 19 - Massachusetts|
|May 16-17 - Lincolnshire|
|May 13 - Ontario - caused by earthquake|
|May 12 - Tennessee|
|May 11 - Abergavenny, Wales|
|May 7 - Florida - caused by secret military mission|
|April 25 - San Diego|
|April 17 - Michigan|
|April 15 - Michigan|
|April 9 - Maine|
|April 3 - Texas|
|March - Vermont|
|March 27 - Cornwall|
|March 26 - Arizona|
|March 25 - Gordonvale, Australia|
|March 22 - Wisconsin|
|March 13 - Virginia - caused by earthquake|
|March 12 - New York|
|March 11 - Kentucky|
|March 5 - Montreal|
|March 2 - Nottingham|
|February 27 - Louisiana|
|February 13 - Ohio|
|February 12 - Indiana|
|February 10 - Pennsylvania|
|January 30 - New Orleans|
|January 30 - Washington D.C|
|January 29 - Maryland|
|January 24 - San Diego|
|January 20 - Swansea|
|January 19 - New Orleans|
|January 18 - North Carolina|
|January 17 - Canterbury|
|January 16 - Beddgelert, Wales|
|January 16 - Greater Manchester|
|January 13 - Marseilles|
|January 12 - North Yorkshire|
|January 6 - Louisiana|
|January 6 - Oregon|
|January 5 - Liverpool|
|January 4 - Missouri|
|January 4 - Washington|
|January 3 - Connecticut|