New Delhi: As the search for alien life becomes more intense and reaches newer dimensions with more mysterious, unexplained evidence surfacing, a video has further stumped people by recording strange noises over the Nevada US Air Force base.
The video was posted on YouTube by channel UFO Seekers and has racked up more than 40,000 hits already.
The footage shows two fighter jets flying over the infamous airspace, leaving strange trails as they cut through the Nevada skies at speeds of up to 1,500mph, Dailystar.co.uk reports.
However, just as one stealth plane speeds away, a frighteningly loud double thumping sound can be clearly heard.
Conspiracy theories have claimed that the sonic booms show the CIA is secretly testing alien technology or hypersonic aircraft.
As per the Daily Mail, the loud cracking sounds are caused by shock waves produced when aircraft travel faster than the speed of sound.
Some users even reported seeing a burst of flames burst from the plane's engines.
YouTube commentators claimed the flybys were a cover-up for work on extra-terrestrials within the base.
Check out the video below:
(Vidoe courtesy: UFO Seekers/YouTube)
Area 51 is a US Air Force Base around 80 miles (130 km) from Las Vegas, and is thought to be used in the development and testing of experimental military aircraft.
The heavily guarded area is also is at the centre of many alien-related conspiracy theories.
The US government only admitted the base exists in 2013 after a Freedom of Information request.
The facility had been used during World War Two as an aerial gunnery for Army Air Corp pilots.
Famous machines developed there include the U-2 spy plane, SR-71 Blackbird, and the F-117A Nighthawk stealth fighter.