From Wikipedia, a universal horror:
The space roar is a radio signal from outer space...
Described as a loud hiss, the team discovered the signal while trying to find traces of heat from first generation stars...
[T]he "space roar" sounds six times louder than what is predicted from those sources.
Where does it come from? It's a mystery:
Scientists have yet to explain its source. NASA scientists have currently ruled out primordial stars and all other known radio sources.
Obviously it's the howling of an elder god.