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

[RyuDragnier]

I would say, if anyone might have had any idea about the Sound's origins and the determination to quell it, that would be Azem. It was part of their role as Wanderer, to know the star and any threat to it. If Hydaelyn had meant to be a solution, Azem would have not rejected Venat's invitation to join them. No, I think Azem set out to find the origin of the Terminus, but as we know, whatever they might have uncovered was lost when they were sundered. Yet, who knows. Perhaps the key resides in us and whatever memories of Azem we possibly regain. That would be certainly interesting.

It'd be very interesting if we had discovered it, and revealed it to Hydaelyn right before we were Sundered. Remember, Midgardsormr had a pact with Hydaelyn and was protecting something in Silvertear Lake, whatever is there is incredibly important to what's going on. Whether that's the path to Hydaelyn herself, the seal to the cause of the Sound, or something else entirely is the question.