Djpekingman great film, and a really interesting area of WW2. The young men that were in the U-Boats in the last few years of the war had a life expectancy of 40 to 60 days. Brutal conditions.
I'm not 100% sure. From what I've read on the web, the sounds were rhythmical & 30 mins apart, so more than likely human & an attempt to give a location.
I've also read that they were made by pieces/chunks falling off the structure of the Titanic as it corrodes.
The worst case scenario is that the sub got trapped/damaged at the bottom of the sea, and then imploded within the last few hours due to the sustained pressure.
