For some reason Ubuntu 8.04 and later come with this Pulse Audio pain in the ass. I'm not going to sit here and rip on it because it's not a bad little sound device, it's just improperly used. Anyway I was googling around the internet and found a website (see below) that tells you the command needed to disable it. Any time you want pulse audio disabled just enter "killall -9 pulseaudio" and that should correct everything. If you find having Pulse Audio disabled fixes your problems then I would suggest having that command execute at start up by opening your preferences, clicking "Start Up Applications" and adding the command in there.
Here's the site I got this off of:
http://tycheent.wordpress.com/2009/03/3 ... ulseaudio/