In the sound clip that was on the website the guy said something is happening in deep space. As we know the ark is in deep space so that could possibly be hinting that we could be going back to the ark. However that is just my theory and may be proven true or false in the upcoming weeks.

I think it’s a reference to the attacks on the human colonies, as described in the Halo 5 description: “Peace is shattered when colony worlds are unexpectedly attacked. But when humanity’s greatest hero goes missing, a new Spartan is tasked with hunting the Master Chief and solving a mystery that threatens the entire galaxy.”

The UNSC is probably keeping the attacks as classified as possible to prevent mass hysteria breaking out among the planets since the Human-Covenant War began the exact same way. So when he says “something is happening deep in space” I think he’s referring to whoever/whatever is attacking us.

“Deep Space” is a very relative term that can literally mean anywhere not directly in Earth’s galaxy.