Can't hear zombies sound.

When i spawn any zombie or alien, they are with no sound. Only combines’ sound work and citizens’ sound work. Do i have this problem only, or somebody else got this thing? How can i fix it?

It’s because you don’t own HL2. HL2:DM does not count. The original is a necessity for this ‘mod’(game :p). Buy it and download it ASAP.

Thank you for notice.
UPDATE: I had sounds about 6 month ago and after i reinstalled my gmod server, all sounds gone.
P.S Sounds work in single game

Believe me, get HL2 and it will work 100%.

Now i found it:

Here’s Weapon pack, where is fix for missing npc sounds.
I post this because if somebody other get same problem

Thanks anyway for help

Lol ok, enjoy playing GMod with the stock shit only