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

[Kesey]

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?)

I mean they could have set the "apocalypse" in motion and Zodiark stopped it. Our defeat of Zodiark (I'm not alone in thinking this showdown is coming, right?) may set it off again. Destroying the great evil only to reveal the greater evil behind it huge jrpg trope. Guess we'll wait and see.