Hey there, I think I found a clue as to the deep groaning.
So I was watching Speaker's Network newest lore dive video (https://www.youtube.com/watch?v=r87PZIhZ_vY). In that video, he uncovers a Koji interview about some obscure 1.0 lore.
Ok, this is only a clue and it's purely speculation, but I think this could be relevant. (https://youtu.be/r87PZIhZ_vY?t=765) There's a presence UNDERNEATH Silvertear Lake that the 1.0 story was supposed to unearth. Here's a quote of the interview:
"That was related to the whole, 'what lies deep beneath silvertear?' Yes, something stopped His (Gaius) advance, and then there was the trailer beam, tons of primals shooting out. And then there was the seal. What is it sealing? What was going on in there?"
"[...] Whether that was enough to seal off something that was already sealed, but the seal was getting weak, or.. that I don't know. There could be something like that. The hint that Gaius was stopped for a reason, and that it was a powerful force. There's a presence. It wasn't just Midgardsormr there, it was more of a force [...]"
Seeing as how Silvertear is this massive pool of aether and sort of a soft spot concerning Hydaelyn.. enough of an opening she made a deal with Midgardsormr to get him to guard it is really interesting.
Now, this could've all been repurposed to describe Hydaelyn's presence down there for the story with Midgardsormr and Heavensward. This all also could've been dragged out and put into Shadowbringers and repurposed there as something else. Still, this sounds earily similar to the deep groaning within the planet that was referred to in the fall of Amarout.
I think this 'deep groan' is still in the planet and I wouldn't be surprised if it is tied to Silvertear. Maybe that's how Graha was able to teleport the tower through the rift(?). There's a common link between that location and all of the other reflections. Who knows, but super stoked to run across this neat tidbit of info![]()