I'll bet you it isn't your sound card at all. Have you overclocked your CPU or video card any? Check the temperatures on them like Mammikoura said. When I was having a few stability problems with my computer when overclocking, when playing Far Cry everything would freeze (no artifacts though) and the sound would repeat a split second segment over and over again, but I also use onboard sound (I really need to upgrade that
). So, just check your temperatures and voltages if you have overclocked, if you have then the voltages may be a little too low to keep it going that far since the power lines do fluctuate a bit. It could be just dropping too low after pumping that much power while playing games for that long.
Sorry, that's probably hard to understand no thanks to my not-so-excellent sentence construction there (
) but I hope it helps anyway.