No Zombine sounds

The zombines have no sounds even the foot steps are missing. So what can i do to fix this?

This will annoy the crap out of you, but you should try “verify integrity of game cache” for Garry’s Mod, Half-Life 2 and Half-Life 2: Episode One (Episode Two is optional since it uses Zombine NPCs as well chance it will help is 1 to 10). Hopefully one of them is corrupt and will update itself.

It will annoy you because it will take quite some time of waiting during the verification.