How do I get to the Ambient noise files for left 4 dead?

Title says it all, I would like to know how to access the ambient sound files for l4d. Where in the directory is it?

Also, how would one go about creating ambient sounds?

I don’t have L4D, but my guess is its in the “sound” folder under “ambient” of the GCF. Also, if I remember correctly from the last time I played L4D, they used some ambient music from HL2, which would then be in the “Source Sounds” GCF.
You need GCFScape to extract the files.

And for your second question:

EDIT: If you’re mapping for L4D, you just follow the instructions on the above link. Sorry for the confusion.