Missing pcm0 and speaker devices - what's the best way to troubleshoot devfs?

[Scott Spare]

1. A month or two ago, /dev/speaker disappeared.  Kldstat still says the
speaker.ko module is loaded, but /dev/speaker is missing, and commands like
"beep" no longer produce any output. (/dev/speaker: cannot open for
writing.)  However, the speaker can make sound -- it beeps when the machine
loads, or when I do a ^g.

2. About a week ago, the sound card stopped working.  It's an M-Audio
Audiophile 24/96.  The modules for the card are listed (sound.ko and
snd_envy24 when I do a kldstat, but /dev/pcm0 is missing.

Any idea what's going on here?  A reboot seems to cure problem #2 for a
little while, then it breaks itself again.  dmesg offers no clues.

uname -a
FreeBSD fqdn.com 7.2-STABLE FreeBSD 7.2-STABLE #1: Fri Jun  5 17:22:05 EDT
2009     root at fqdn: /usr/obj/usr/src/sys/SCOOBY  i386