freebsd stable - Oct 2008 - What could be causing unexpected reads to acd0?

I'm seeing this sometimes before my machine dies:

Oct 26 03:28:00 belle kernel: acd0: WARNING - READ_TOC taskqueue timeout -
completing request directly
Oct 26 03:28:00 belle kernel: acd0: WARNING - READ_TOC freeing taskqueue zombie
request
Oct 26 03:30:00 belle kernel: acd0: WARNING - READ_TOC taskqueue timeout -
completing request directly
Oct 26 03:30:00 belle kernel: acd0: WARNING - READ_TOC freeing taskqueue zombie
request
Oct 26 03:32:00 belle kernel: acd0: WARNING - READ_CAPACITY taskqueue timeout -
completing request directly
Oct 26 03:32:00 belle kernel: acd0: WARNING - READ_CAPACITY freeing taskqueue
zombie request

I run the gnome desktop environment.  Could it be that?

I do not have this mounted.  The only thing that's running around this time
is /sbin/dump.  I'm never at the machine when this happens.

FreeBSD belle.0lsen.net 6.3-STABLE FreeBSD 6.3-STABLE #0: Sun May 25 21:55:57
PDT 2008     root@belle.0lsen.net:/usr/obj/usr/src/sys/GENERIC  i386

Thanks,

-Clint

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Sorry, I've just joined the stable ml.

Is the problem that is happening to you, something similar to what is described
here (and linked threads)?
http://www.freebsd.org/cgi/query-pr.cgi?pr=128076