Left 4 Dead 2 Soundtrack - 'WAM!'
[To listen in higher quality, add &fmt=18 to the end of the URL address.]
Location: C/Program Files/Valve/SteamApps/common/left 4 dead 2/left4dead2/sound/music
Official Site: http://www.l4d.com/home.html
Left 4 Dead 2 is © Valve