I had the same problem with Sins on this old computer I'm using temporarily (Pentium 4 2.4GHz, 1GB RAM, 128MB Radeon 9200). What I did to fix it was to first update the Realtek AC97 drivers, but I also turned down the DirectSounds Acceleration from Full to Basic. Since then, sound has been fine. Try to make sure either the drivers are up-to-date, turn down the DirectSound Acceleration, or both.