A very peculiar thing here. My perfectly working ubuntu 9.04 64 bit T400 laptop lost its sound - well not exactly "lost" but certainly it was not working. It used to work perfectly but now just generates what appears to be static!!!
I had not used sound for a while and done quite a few things to my laptop so it was not clear what could be the culprit. I had thought maybe the sound card had blown or some other disaster but it turns out that the fix was incredibly simple.
I just opened the speaker volume control from the icon at the top of the gnome screen and chose "Volume Control". For some reason my "PCM" sliders were at the bottom. I just moved the slider to the top and sound is back to normal again.