When I listened to the audio file and heard that eerie tone I got shivers, it was epic. I really hope that is part of the main soundtrack, I think it really fits a mysterious and alien mood. That is what a Halo soundtrack should be, and I recall the words Marty O’Donnell was given for the original trilogy soundtrack were “Ancient, alien, mysterious”.
Some of the SFX were certainly unsettling. Could definitely work with a Flood level, but I don’t think it qualifies as a full part of the soundtrack.
I didn’t find it epic at all. It was good, and intriguing, and perhaps it’s not even going to be featured in the final game, could be just for the Arg…
I think the soundtrack is going to have a central theme often heard in the Halo 5 beta menu and the Behind the Scenes video at around 7:00. The music in the audio files doesn’t seem to fit with what we’ve heard so far, but it would be interesting to hear a variety of sounds in the game.