Singing Grunt

In the Halo 5: Guardians level Enemy Lines there is a lone Unggoy sitting on a ledge, singing to himself.

Overview
The Singing Grunt will sing for roughly 20 seconds, and then will stop. He will not acknowledge the player, and can be killed with ease.

Trivia

 * This is the second Easter egg of Halo 5: Guardians that revolves around a Grunt on a ledge.