Halo: Reach Easter Egg - Sgt. Buck from Halo Reach

To find this, You have to be on Legendary, with IWHBYD on.
On the level where you fly around in a Hornet, near the beginning, you may hear this....
"KSSHK! This is SGT Buck asking for assistance."
"We'll send help right away."
You then assist SGT Buck to where he needs to go; if you get out where he gets out, you can clearly see that it is SGT Buck from Halo: ODST....He will walk into a dark hallway and say "See you in hell, Spartan."