The banging sounds were picked up during the search for the Titan submersible which went missing last year.
Back on June 18th, 2023, the undersea exploration vehicle, which was carrying five passengers including Stockton Rush - CEO of OceanGate Expeditions which was running the operation - disappeared after embarking on a trip to the wreck of the Titanic situated 12,500ft beneath the sea.
What followed was a multi-day search by rescue teams alongside extensive global coverage as people around the world waited with baited breath to see if the crew of the submersible could be located.
Ultimately, though, the discovery of a debris field a few days later confirmed the worst - the submersible had violently imploded, killing all five passengers.
The incident highlighted a range of safety failings by OceanGate, along with a multitude of technical issues with the sub itself, while putting the entire future of Titanic wreck expeditions into doubt.
One mystery that still remains concerning the loss of the sub centers around the detection by sonar devices of a series of unexplained banging sounds within the vicinity of the search area.
At the time, it was speculated that this could be the sound of the stricken passengers of the Titan submersible banging on the inside of the hull to attract the attention of the rescuers.
Now, for the first time, the audio recording of the banging sounds has been released by the Canadian Air Force as part of a new UK documentary - Minute by Minute: The Titan Sub Disaster - which is set to air on Channel 5 on March 6th and 7th.
You can also hear the recording in the news video below (skip to 00:27).
"The symmetry between those knockings is very unusual," said former Navy submarine Captain Ryan Ramsey. "It's rhythmic, it's like somebody is making that sound, and the fact that it is repeated is really unusual."
But if it wasn't the Titan sub passengers making the sounds, who or what was ?