I just realised that the sound on my Futitsu Siemens Li2727 laptop had stopped working - probably when I upgraded to Ubuntu 8.10, but not sure.
All you get when you play sound is crackling.
Dmesg gave the following:
[ 13.411005] HDA Intel 0000:00:1b.0: PCI INT A -> GSI 22 (level, low) -> IRQ 22
[ 13.411038] HDA Intel 0000:00:1b.0: setting latency timer to 64
[ 13.442811] hda_codec: Unknown model for ALC268, trying auto-probe from BIOS.
The 'Unknown model' looked like a problem, so I spent a while searching for solutions to do with this, but to no avail.
Found a bug report - https://bugs.launchpad.net/ubuntu/+source/linux/+bug/281322, which sounded like my problem, but was solved by adjusting alsamixer.
When I used alsamixer I only saw a single channel, which I think was the PC speaker, so it didn't sound right. Looked at https://wiki.ubuntu.com/DebuggingSoundProblems which said there was another program, gnome-alsamixer. Tried this and it showed me lots of different sound card channels. The volume of the PCM channel was zero - setting this to full volume cured the problem - Solved!