Part of me has been wondering if the noises being heard might be an unexpected discovery of a military (Russian, Chinese, US) submarine operating in the general area. Don’t they submerge for long periods of time without comms?
https://navalpost.com/how-deep-can-a-submarine-dive/ The depth limits of the most known nuclear powered submarines’ depth limits, as follows;
Typhoon-class: Test depth 900 m (3,000 ft) Astute-class: Over 300 m (984 ft 3 in) Akula-class: 480 m (1,570 ft) test depth for Akula I and Akula I Improved, 520 m (1,710 ft) for Akula II and III, 600 m (2,000 ft) maximum operating depth Ohio-class: Test depth >240 m (800+ ft) Virginia-class: Test depth >240 m (800+ ft) Borei-class: Test depth 950 m Rubis-class: Test depth 350 m Barracuda-class: Test depth >350 m
We really don’t know what depth the noise was comming from.
That being said it is vanishingly unlikely that an unrelated submarine trying to remain stealthy would be banging on their hull every half an hour.
The Titanic is at 3800 meters. That it's reachable, by private organizations no less, is just a marvel.
That's also why military specs on things like this are always lies, you don't want anyone knowing how deep you can actually go, which likely includes most of the crew.
https://www.iflscience.com/for-15-years-sweden-thought-enemy...