town_warehouse is a sound you can find in the game files for the Half Life 2 mod 'Missing Information', it's a reversed sound of the strings of an instrument being plucked at and the sound quickens but slows back down
You do actually hear this somewhere in Missing Information's Ravenholm, but you may have to be listening very carefully or noclipping to a certain area on a roof where you can hear it better
Location
http://www.youtube.com/watch?v=4j1k3z-ZQy0
Original sound
http://www.youtube.com/watch?v=GUsF1uubs1k
Wow man...
I'm tripping balls
Tanker160 1 month ago