Sometimes, a sound card can brake your whole system (yes, brake, not break, though that might happen too
).
Especially OnBoard-Soundchips tend to look like hardware sound processors, but really leave most of the work to your CPU, or, if they are actual hardware sound processors (in terms of environmetnal effects and directional audio), they could lack calculating power, so slowing down the whole game.
I had a similar problem in the King Kong game, where the game would slow down to a slide show when too much stuff happened at the same time.
In Penumbra, I experienced a dramatic framerate drop after I turned on the generator until I left it's room, but the rest of the time, the game ran smoothly even on highest settings.