audio no longer produces sound

[David Roundy <droundy@civet.berkeley.edu>]

I made an unfortunate discovery today that audio no longer works on my
laptop (a Thinkpad X21, which is running testing).  I had it working a
month or two ago, but haven't used audio much since, so I don't know when
it stopped working.  In fact, I had it working both for recording and
playing sound.

I've been testing it using both `play test.au` and 
`cat test.au > /dev/audio`.  I also tried running timidity on a midi file,
as well as festival (which was how I found out I had this problem).

I checked that the devices exist, and I ran aumix to see that the sound
output is actually turned on.

The sound card is a CS4281, and support for it is compiled into my kernel.
Just in case, I tried rebooting with several older kernels, in case
something broke recently in the kernel.  

I am at the end of my rope here, and am very frustrated.  :( Any ideas as
to how I could go about trouble-shooting this would be greatly appreciated.
-- 
David Roundy
http://civet.berkeley.edu/droundy/