Edit: Sound can be a PITA on linux.
Check out this current thread: viewtopic.php?f=48&t=110044
And in case you don't get a better answer -
- I've had VLC sound bad and everything else sound OK (choppy - silence and sound alternate a couple of times/second). Try different programs.
- Run "alsamixer" and make sure volumes are high enough
- I always need to install "pulse" and "pavucontrol" to "record what you hear", and it seems to solve other problems.
- Perhaps reinstall "alsa" and associated parts.