So I was reading through the Osirus grimoire card and I found this quote:

I hear stories of Lord Shaxx meeting with fireteams of Warlocks who have no shadow and never blink. Of jumpships slipping into the Reef on cold trajectories and meeting no intercept. Of questions hidden in matter engrams and answers decrypted on distant battlefields.

That sort of sounds like the mysterious transmissions we receive while on patrol. I had always assumed it was supposed to be something from Rasputin, but perhaps it's Osirus?