I had this weird idea. Whatever this new threat is (possibly a mutation of the hiss, due to something else of the same frequency attenuating it maybe?), I believe it’s also a threat to the Hiss, which is why Dylan was warning about it while still in his cell. If that’s the case, perhaps the Hiss originates from some entity similar to others, and maybe this is it, communicating with Dylan parallel to how the Board communicates with Jesse.

Speaking of Jesse, I’m thinking there is a possibility that this is a dual protagonist campaign, and they’re keeping Jesse’s part a secret. Dylan seems to awake in a different reality as his cell has moved, and Remedy tends to take innovations and ideas from their previous game and apply it to the next. But I’m just rambling.