The haunting knocking sounds heard beneath the Atlantic Ocean during the frantic search for the Titan submersible and its occupants last summer have been unveiled in a chilling new audio clip.

Reports emerged on the second day of the search that banging noises, resembling someone “knocking” against metal, were echoing from the depths at 30-minute intervals after the underwater craft lost contact with its mothership on its journey to the Titanic wreck.

An upcoming British documentary titled “The Titan Sub Disaster: Minute by Minute,” set to air on Channel 5, played the eerie audio clip for the first time, reigniting memories of the desperate search.

Former Navy submarine Capt. Ryan Ramsey, featured in the documentary, commented on the peculiar nature of the rhythmic knocking: “It could be somebody knocking. The symmetry between those knockings is very unusual. It’s rhythmic, it’s like somebody is making that sound, and the fact that it is repeated is really unusual.”

Initially, hopes surged among searchers that the sounds might be signals from the lost mariners. However, it was later concluded that the noise couldn’t have originated from the sub’s passengers and crew, as they perished instantly in the sub’s catastrophic implosion two hours into its voyage.

The source of the knocking remains a mystery, leaving investigators puzzled about its origin. Speculations ranged from the ocean’s natural phenomena to activities of other vessels in the vicinity.

The discovery of the debris from the Titan sub, located about 1,600 feet from the bow of the Titanic shipwreck, shattered hopes for the families of the missing crew members. The Coast Guard confirmed the presence of “presumed human remains” within the wreckage ten days after the sub vanished on June 18.

Among the victims were OceanGate CEO Stockton Rush, French Titanic expert Paul-Henri Nargeolet, British billionaire Hamish Harding, and Pakistani businessman Shahzada Dawood and his son Sulaiman Dawood.

Rush, who was piloting the submersible, faced scrutiny for alleged safety oversights regarding the vessel’s readiness for tourist voyages to the Titanic.

As officials continue to probe the evidence recovered from the recovery missions, an impending public hearing on the incident is anticipated to shed further light on the tragic events surrounding the Titan sub disaster.