It is a non-understandable language interrupted by bursts of static. The signal is on a loop, like an automated distress beacon. When reversed and slowed down, it says "the alien is never alive" (Also near the end you can hear it say "help me, help me") which is a reference to the fact that the concept of humanity making first contact through a dead alien is often found in works of science-fiction. Because of its limited range, a player can easily track the signal to its source. See the article on the alien crash site for much more information.