I've 2 exact same PCs with Fedora 8. One of them has audio (call it PC1), but the other does not (PC2.)
The one without audio (PC2) happens to have the following device listed in lspci:
01:05.2 Audio device: ATI Technologies Inc Radeon X1200 Series Audio Controller
Subsystem: ATI Technologies Inc Radeon X1200 Series Audio Controller
Flags: bus master, fast devsel, latency 64, IRQ 19
Memory at fdcfc000 (64-bit, non-prefetchable) [size=16K]
Capabilities:  Power Management version 2
Capabilities:  Message Signalled Interrupts: Mask- 64bit+ Queue=0/0
Kernel driver in use: HDA Intel
Kernel modules: snd-hda-intel
This doesn't appear on the PC with sound (PC1). So from Gnome -> System -> SoundCard Detection, there appears only one sound device (ATI SBx00 Azalia) in PC1, but 2 devices (ATI SBx00 Azalia and ATI Radeon X1200 Series Audio Controller) in PC2.
Sound test on Azalia on both PCs do play sound, but PC2's X1200 Audio has no audible sound. I'm guessing pulseaudio is somehow using this X1200 Audio as default device in PC2.
The question is, why does X1200 Audio appear in PC2 but not PC1? I checked all BIOS settings and there just is no difference between the two. I'm guessing ATI X1200 is a video device, not audio.
How do I make pulseaudio use ATI SBx00 Azalia as the default sound device?