OK so I was using GCFScape to find the end song of portal 2 and found it tucked away in C:\Program Files\Steam\steamapps\common\portal 2\portal2 and it is called pak01_dir.vpk then look for portal2_want_you_gone.wav Anyway, I listened to all the other tracks and found some really strange ones: sp_a1_intro3_r1 sp_a2_bridge_the_gap_r2 sp_a2_pull_the_rug_r2 sp_a2_trust_fling_r2 When I open them with an audio editor they look almost, if not exactly, identical. I've played around with reversing, inverting, slowing and speeding them but they still sound like nonsense. I'm sure I can make out the odd word but that may be my imagination. I suspect they contain some kind of hidden message as I don't remember hearing them in-game. And another slightly weird one which sounds a bit like GLaDOS asking for help or something: Listen to them for yourself, what do you think? Off topic but I also found some quite cool ones: sp_a2_dual_lasers_r1 - some strange song i can't quite make out. sp_a4_finale4_z2 - Awesome remix of main theme.