I upgraded my Fujitsu-Siemens laptop to Ubuntu 9.04 from 8.10 a few days ago.
Everything worked fine except for sound. Sound went from working perfectly in 8.10 to being quiet, and awfully crackly in 9.04.
If I updated the gnome settings to use OSS rather than ALSA it worked ok, except flash movies still made crackly noises (I don't think flash can use OSS).
I messed about with the gnome mixer without luck, except I did notice that changing the PCM volume did nothing (which is wrong), but changing the 'beep' volume did alter the sound volume (Along with crackles).
I don't know why the beep and PCM are the wrong way around, and don't have time to work out how sound works properly, so I went for brute force and ignorance - I had heard a suggestion that Pulseaudio might be the problem, so I replaced pulseaudio with esound, and it all seems to work now...
Therefore, I don't know what the problem was, but it was cured by getting rid of pulseaudio...
