There are 3 theories for the banging sounds heard in the search for the Titanic sub. None has expert

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The noises have raised the hope that the five passengers on the Titan sub are still alive.
But experts disagree on whether the noises could have come from the sub.
The noises could be coming from the crew, the Titanic shipwreck, or marine wildlife.

Underwater noises detected in the search-and-rescue mission for the Titan submersible have offered hope in finding the five crew members trapped inside.

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The US Coast Guard confirmed Wednesday it picked up suspicious underwater sounds using sonobuoys. Some reports say the banging sounds were heard at 30-minute intervals.

As rescuers race to find the source of the noise, experts remain divided over whether the sounds are from the sub or something else entirely.

Here are the leading theories about what could be causing them.

1. Crew members trapped in the Titan are banging on its hull

The search for the Titan submersible that has been missing since Sunday has now picked up pace, with experts predicting the crew may have run out of their available oxygen reserves.

If a report by Rolling Stones is correct, the noises were heard in a pattern, with banging detected every 30 minutes. This could point to a human source.

"There's not a lot in the natural world we can think of that would do that every 30-minute cycle," deep-sea explorer David Gallo told ITV's Good Morning Britain.

"We have to, at this point, assume that's the submarine."

Stefan B. Williams, a professor of marine robotics at the University of Sydney told Insider banging on the hull has been used by marooned submariners before.

"There have been reports when there have been issues with submarines where the sailors will bang on the hull and that acoustic noise will travel," he said.

Frank Owen, a submarine search-and-rescue expert, told the BBC his "confidence went up by an order of magnitude" when he heard the reports.

Crewmembers onboard might be familiar with protocols to attract attention from the surface, including seasoned underwater diver PH Nargeolet, he noted.

2. The noises are coming from the Titanic shipwreck

A shot of the Titanic wreck in 1996. Xavier Desmier/Gamma-Rapho/Getty

Not everyone agrees the noises could be made by the crew.

The hull of the submersible is said to be made of carbon fiber, which would more likely make an undetectable "dull thud" than a tapping noise, Former Rear Admiral Chris Parry, a retired officer in Britain's Royal Navy, told Talk TV.

The sonobuoys' operators would be trained to differentiate noises typically heard in the ocean from noises made by trapped survivors. But the Titanic shipwreck itself may be sending out its own noises, some experts claim.

"You get a lot of mechanical noise in the ocean," Parry told TalkTV. "Trying to differentiate it from tapping noises, as it were, I'm afraid is a fool's errand."

Matthew Schanck, search and rescue expert and founder of MarSAR International told Insider Wednesday: "We've gotta be cautious not to get too excited that this sound is coming from the craft,"

"There's a massive metal wreck down there — the Titanic — the banging could be something as simple as a piece of that moving in the current or something to do with the wreck itself," said Schanck.

Even if the wreck isn't making the noises itself, it may be changing the sounds that would naturally be picked up underwater, Jeff Karson, Professor Emeritus of Earth and Environmental Sciences at Syracuse University told MailOnline.

"One possibility is that the sounds bouncing around the debris. And so it's a more complicated echo," he said.

3. Marine life could contribute to the background noise

One possibility is that marine wildlife "like whales" could be contributing to the noises, said Williams.

However, it's likely the operators would be trained to distinguish these from noises made by the crew, Carl Hartsfield, a laboratory director at Woods Hole Oceanographic Institute, told The New York Times.

"From my experience with acoustics, there are sounds by biologics that sound man-made to the untrained ear," he told The New York Times. "But I can assure you that the people listening to these tapes are trained."

The sounds are the search team's best hope of finding the sub

Even if experts disagree on whether the noise could be coming from the submersible, it's somewhat of a moot point, Schanck said.

"We have no way at this stage of proving that that noise is coming from the craft, but in search or rescue, you have to use whatever you get given to your advantage," he said.

"For instance, on a surface search, if you are looking for a person in the water and you find a shoe floating, you use that as a sign," he said.

"That's information we can use to try and narrow our search area down," he said.

The First Coast Guard District has deployed remotely operated vehicle equipment to a site where it thought the noises could have been coming from, Capt. Jamie Frederick, the response coordinator, said per CNN.

But searches in the area have "yielded negative results," and an analysis of the data picked up by the sonobuoys has so far been "inconclusive," Frederick said per CNN.

"We don't know what they are," he said.

Still, the US Coast Guard told Insider Thursday the search will continue even beyond the time experts have estimated the oxygen would run out.

"We have to remain optimistic and hopeful," Capt. Jamie Frederick, the response coordinator for the First Coast Guard District said during a news conference Wednesday, per CNN.

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