I’m pretty sure that’s the sound of a Chinese sub-launched missile.
Seriously, though - a YouTube video? Anyone can use a computer to make a spooky sound, then mix it into a video clip and claim it was recorded in the wild.
True but a lot of people world wide are reporting it and recording it.
I am sure there is a reasonable explanation for it.
Especially when they embed pay-per-click ads into them.
Clever.