If you were a hyper advanced alien civilization, rather then mucking about with noisy electromagnetic waves, perhaps you would try to make contact with other intelligent life forms by sending your messages via neutrinos.
First detected in 1953, neutrinos pass easily through most matter making it possible for your signal to pass through the Milky Way without being blocked by stars and interstellar dust. They are also not subject to the "noise" of optical and radio waves traveling alongside them through space.
How frickin' cool would it be if the ancient astronauts were actually some weird insterstellar beam blasting our brains with cosmic super-intelligence? Screenwriters, get cracking!