I personally believe it's more broad. Because if it's the deep sea metro, it mean it was hinted at before the Octo Expansion was even planned.
So for me, I think it's more possible that what we're hearing is Octolings doing their own things. The clinging and breaking could be Octolings working on weapons, technological devices and so on. The scream could be from anything, ranging from octos fighting to them being born. The laughing might as well be them having fun.
After all, it was proven that Octolings and the Octos don't suffer or anything, they have a fun live, sure there's constant war, but they are shown to have civilisation, high degree schools and normal lives. So it wouldn't be far fetched to believe what we're hearing might just be the Octocivilisation. But that's probably just me, lmao.