For me, this problem manifested itself after changing the graphics card. I have a new PC with a freshly installed Windows 7 64-bit. As the last component in the new PC I exchanged the graphics card. Specifically the Radeon 7950 instead of Radeon 6950. The drivers I had installed the latest, so in addition to the physical exchange of cards I did not change anything. But after the exchange I noticed problems with up to seconds long lags. Also I can seen stuttering.
Because it seemed that the phenomenon occurs with certain sounds (not just PPSh), I tried the following:
1) disabled the sound output on Radeon
2) set the sound option in the game to default settings (with the original video card was set to max)
After these adjustments, I got rid of lags but still appears mild stuttering. From time to time the game freezes so that the video is frozen, the game does not respond to input but the sound still goes on in the background.
I tried other currently installed games (Shogun 2, Metro 2033, Mafia 2, Deus Ex HR, etc.) and those running without problem.
For your information - I do not use overclocking and using a separate sound card (Sound Blaster X-Fi Titanium Fatal1ty Pro).