The Covenant Music Glitch

After defeating both Scarabs on The Covenant, go up on the left ledge of the Citadel. Make sure you are still in your Hornet. Get out on the ledge when you can, then go as high as you can. When you get high enough, this non-Halo 3 music featuring a pianist plays. One thing to do with this is start sobbing, then jump off and committ suicide. Make sure you have a checkpoint after you defeat the Scarabs.

Multiplayer
This glitch is only recommended for 3 or less players, due to the capacity of the Hornet. Take only one Hornet up, then unload the passengers. Then get out yourself. If you get out first, the passengers won't have time and they will die with the Hornet. Go up in a single-file line. Only one player needs to reach the top for the music to play.