Enable Mute in Zombie Panic: Source

Zombie Panic: Source (official site) is a multi-player mod for Half Life 2 that pits human survivors of an undead holocaust versus ravenous flesh-eating zombies. Though officially still in beta, it is quite playable and is already loads of fun.

UPDATE: The issue below has been fixed as of version 1.2b - You can download it here.

There are, however, still some kinks that need to be worked out. For instance, as a zombie you will always see survivors aiming to the side even though they are shooting at you - though it's not hard to ignore, this graphical bug can be disorienting when you're chasing down your dinner - I mean other players. Poorly-designed maps and getting stuck in place are other such experiences. But after all the beta version of the mod was just released less than one month ago, so in time these issues will be worked out.