Comment 2 for bug 476652

Sounds very similar to my experience.

I did an online upgrade from Jaunty to Karmic two days ago. No sound problems before but masses after.

When playing video (using Kaffeine) sound would be ok for 3 to 20 minutes then disappear into clicks, followed by silence. Using 'System Setting -> Multimedia' I told the system to use the CMI8738 module rather than pulseaudio & this appeared to cure the problem, for a day.

When playing games (Vendetta Online) the system degenerates into clicks after 5 - 20 seconds, shortly followed by complete silence. Possibly related, as this problem cropped up at the same time, when I try to exit the game the system locks up & I have to do a hard reset. Before the sound problem VO behaved perfectly.

Now, on system startup, KDE reports that the modules have been removed leaving only pulseadio available.

I tried to get more debug info but there a other problems (display settings on startup, dpkg currently unusable) confusing the issue.

My hardware is:-
AMD Phenom x4 CPU
nVidia GeForce 8200 chipset.
Added CMI8738 sound card as onboard sound was low quality. Have switched off onboard sound in the BIOS.

Cheers, Kimdino