Movement is a song included in the Halo 3: Original Soundtrack.
This piece starts with a choir melody. At 0:12 seconds, drums and orchestra joins in and gets louder and louder. The song swells and abruptly ends. This plays randomly in the Main Menu of Halo 3.
It runs for 0:27.
It should also be noted that this song can be heard in the Starry Night announcement right when the Master Chief stands up.