Think of all the sea monster stories told by sailors back in the 1700s... those were likely giant squid.
That was on that list. But I did happen to see a news show where the marine biologists were using the old submarine sonar listening system to monitor and track whales. They would play a tape and the guy would say something like:
That’s a gray whale off the coast of California....
That’s a Beluga Whale in the Bering Straight...
Did several more, and then the last tape - the sound was in between an organic, animal sound and a high frequency electrical, synthesized sound - almost like something from a sci-fy movie (although some of the whale sounds were almost as weird).
The guy said “That is in the Indian Ocean, at a depth of over xxxxx feet (it was REALLY deep),......
...
and we have no idea what it is.”
They played the sound again and a chill ran up my spine.