What exactly do we know as of 5.3 about the sound that was heard before Amaurot fell?

[Cilia]

We haven't learned anything new, but to recap what we do know about the Sound:

• It started somewhere outside Amaurot.
• It spread in some manner; whether radially or like a contagion is unknown.
• It came from the Planet itself, before Zodiark existed as its "will made manifest."
• It caused the Ancients' creation magicks to go haywire, involuntarily forcing them to invoke creation spells making their deepest, darkest fears manifest.
• When it reached Amaurot, it basically caused the apocalypse.
• It was finally halted by Zodiark's summoning, which consumed the lives of half of the Ancients still alive at that point.

Everything else is just speculation, but to throw my two cents in...

I am of the mind that it may have been a reaction from the planet to the Ancients' hubris. Even in contemporary times the few that remained were extremely arrogant until their defeat; adding to this is that Amaurotine civilization takes many cues from Thomas More's Utopia (its existence as a utopia in Emet-Selch's memory; Amaurot; Hythlodaeus; Anyder) - a place that cannot exist in reality. It also has a smattering of Greek in it (Therion the "Chthonic Riddle;" Hades; several Greek words such as Akademia and Utopia), which lends credence to the idea of hubris being a part of the Ancients' downfall (a recurring theme in Greek myth).

The Ancients' refusal to try and understand the Sound, and in so doing try to prevent a recurrence of the phenomenon, is what peeves me the most about how they handled the situation. Instead of learning from the event they just tried to go back to the way things were before. Again, this ties back into their hubris - those who do not learn from history are doomed to repeat it, and the Ancients didn't even appear to want to learn any sort of lesson from the Sound.

Considering G'raha's 5.3 closing narration mentions a "beast" and the "apocalypse," I have little doubt the Sound will factor in going forward; but we still know next to nothing about it. (Given modern peoples aren't nearly as well-versed in creation magicks, would it affect them the same way it affected the Ancients?)