Opening game scene stutter in L4D

I notice a stutter with my game at max.
Not on blood harvest though. I notice it on No Mercy.
But I think it is a game issue.
As L4D is great, but its engine seems to have a good number of bugs to it.

I've never gotten any shuttering in Left 4 Dead. Running it completely maxed out it runs great.

i just got game, running it on a 4830, runs great on max...but i get this stuttering every 15-40 minutes or so..the game freezes and the sound loops. this seems to happen at the worst times (a hunter is about to jump at me) and it stutters, or im about to heal and it stutters, i tried running in windowed mode and turning of the multi core rendering but it doesnt help..

the stutter is exactly like in this video

That's worse than a stutter. That's a pause.