I found another reason for this bug. I use a Thinkpad T60, and as stated on thinkwiki, I added pci=noacpi, acpi_sleep=s3_bios to my kernel to enable suspend mode. After removing this from my grub options and rebooting, the sound worked fine again.
The problems started after the first time suspending the system, but didn't go away after multiple reboots. -- Issues with sound on intel-hda in Edgy (2.6.17) https://launchpad.net/bugs/69620 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
