The ping of an M1 Garand in WaW. Edit: here's a few more: The Ray Gun A PaP'd weapon Getting a Mythic in a REQ pack Getting an Elite in a supply drop The Scavenger Panzer Spawn (Origins) Dog spawns and round SFX Vex Mythoclast Hawkmoon The sound of an MW2 AC130 120mm round being fired MW2 nuke countdown Picking up a Scavenger pack Icebreaker