I actually know of a really good ambient mp3 that ZM could use. I played it in a ZM server and it actually felt creepier.

http://www.tempfiles.net/download/20..._ambiente.html

And regarding the parachutes: They seem like more of a novelty than a necessity but they are fun to have. When the humans para to a unreachable spot and the zombies know how to strafe it actually makes the game more fun, because it isn't the same "make cade, try to shoot zombies past the cade while zombies try to break the cade" crapola.