What were the banging sounds heard during search for Titan sub? Experts weigh in

During the search for the missing Titan submersible, sonar reportedly picked up banging sounds from underneath the water. A memo obtained by CNN said it was unclear exactly when the banging was heard on Tuesday, 20 June, and for how long. More sounds were later heard, but they were not described as "banging."

"Additional acoustic feedback was heard and will assist in vectoring surface assets and also indicating continued hope of survivors," an update read at the time.

While it has not been determined what the banging sounds were, experts have come up with various theories. Carl Hartsfield, an expert with the Wood Hole Oceanographic Institution, told CBS news there could be several explanations. "The ocean is a very complex place, obviously — human sounds, nature sounds, and it's very difficult to discern what the sources of those noises are at times," he said.

Jeff Karson, professor emeritus of earth and environmental sciences at Syracuse University, told Daily Mail that that the noise may have been a "complicated echo" that came from sounds that bounced around the Titanic debris field. "It's just not bouncing off of one thing. It's bouncing off a bunch of things. And it's like, you know, dropping up a marble into a tin can. It's rattling around and that would confuse the location," he said.

They could have also been made by marine wildlife like whales, said Stefan Williams, a professor of marine robotics at the University of Sydney, according to Insider.  

At the time the sounds were heard, a submarine expert claimed it was "encouraging" that the five people on board were still alive. "So the fact that we're hearing banging at 30-minute internals tells me that the people inside are sending a message that says, 'We understand that you would be looking for us and this is how you might expect us to react.' So, it's very encouraging," he said. 

An underwater robot is now combing the floor for debris from the catastrophic implosion of the submersible that resulted in the deaths of five passengers. The deceased passengers were OceanGate's CEO Stockton Rush, British billionaire Hamish Harding, French diver Paul Henry Nargeolet, and Pakistani businessman Shahzada Dawood and his son, Suleman.

Following the tragedy, investigators from the US Coast Guard, the US National Transportation Safety Board, the Transportation Safety Board of Canada, the French marine casualties investigation board and the United Kingdom Marine Accident Investigation Branch have been working closely on the probe.