DragonFlyBSD

The effects are the same whether X is started or not. Setting debug.debugger_on_panic has no effect, the system just freezes. I've attached a "screen shot" of a garbled console screen.

While trying this out, I found two other variations of this:

2) Module doesn't find sound card at first, system freezes at the second attempt to load the module:

root@deimos:~ # kldload snd_hda
pcm0: <NVidia MCP51 High Definition Audio Controller> mem 0xf2300000-0xf2303fff irq 21 at device 16.1 on pci0
pcm0: Audio Function Group not found!

root@deimos:~ # kldunload snd_hda
pcm0: detached

root@deimos:~ # kldload snd_hda

==> freeze

3) Sort of a interrupt conflict when loading the module:

pcm0: <NVidia MCP51 High Definition Audio Controller> mem 0xf2300000-0xf2303fff irq 21 at device 16.1 on pci0
pcm0: <HDA Codec: Realtek ALC260>
pcm0: <HDA Driver Revision: 20071129_0050>
intr 18 on cpu0 at 40001/40000 hz, livelocked limit engaged!

And then keyboard and mouse are no longer usable as interrupt 18 is occupied by the usb controller:
ohci0: <OHCI (generic) USB controller> mem 0xf2304000-0xf2304fff irq 18 at device 11.0 on pci0

When unloading the module via ssh, the system freezes as usual.