The Bloop has been a mystery for over a decade. It was a strange sound recorded in the deep ocean, heard throughout the ocean. That sound, when played at sixteen times its original speed, sounds distinctly like a "bloop." Obviously.
Apparently, the Bloop is the sound that icequakes make. As of right now, the Wikipedia page has been updated to reflect this new information, but still has a link to the List of unexplained sounds. There, it appears under "Specific," then under the subhead "Later identified as Ice."
I'm totally thankful for science and stuff, and in an intellectual sense I'm glad that scientists are still figuring stuff like this out. I mean, that's sort of the point. I liked the Bloop because it was unexplained. But it's not a special unexplained thing. There are plenty of other unexplained things. And if anything unexplained is cool enough, eventually someone figures it out.
Getting too attached to the existence of particular mysteries seems to generally end up sucking.
We've still got dark matter for at least another few months, though, right?