Lament for Pvt. Jenkins
From Halopedia, the Halo wiki
Lament for Pvt. Jenkins is the twelfth track in Halo: Original Soundtrack.
The piece is a tense, moody ambiance piece by string orchestra. The piece opens with a dark, powerful drumbeat, followed by an apprehensive minor chord. Every seven seconds, the drum sounds again, punctuating a change in the chord. The ambiance becomes increasingly disjointed towards the end, featuring the scrambled high notes typical of the Flood, and slowly fades out, leaving a dark air to the scene. The piece is arranged into A Private Service in the Halo: Combat Evolved Anniversary: Original Soundtrack.
It can be heard: