Just a couple of observations from MSQ:

I agree that the "ear-splitting roar" might well be a reference to the whole "sound" thing that brought down the Ancients. Then again, anything remotely mysterious and audio gets speculated to be related to the Sound, so who knows.

Secondly, Y'shtola and Krile go on and on about how Hydaelyn hasn't given guidance to her champions for a long time, and I desperately wanted a dialogue option to tell them we know exactly why. Hydaelyn literally instructs us to ignore Lahabrea's rantings (which is an easy ask, because Lahabrea's rantings are eminently ignorable and demonstrably wrong) in the Praetorium, which should have been the answer to "when did Hydaelyn last talk to you". And in the Praetorium, Hydaelyn sacrifices much of her strength (as confirmed by Lahabrea, who as mentioned may be incorrect) to protect us from Ultima. So there's your answer, Y'shtola.