I had some major sound card problem with Ubuntu Linux, but, it turns out the solution was simple.

The symptom was a clicky noise when I was using sound. It was worse when there were more sounds being played. The card was a SoundBlaster Live.

The solution was to move the sound card to another PCI slot. The problem was that the sound card wasn't getting enough of the PCI bus's resources.

Followup

Ultimately, I ended up getting an inexpensive CMI-based sound card (an AOpen AW-840). This worked a lot better, and seemed to play better on the PCI bus.