Comment 24 for bug 479296

Similar freezes here since I upgraded to Karmic. I never had such a problem with Jaunty (or any previous version).
The typical freeze is a severe one (everything really dead, keyboard LEDs don't toggle, soft power off does nothing, forced power off needed).
The last items present in the log is always something like this:
Nov 18 07:49:18 Philinux pulseaudio[1854]: ratelimit.c: 5 events suppressed
and the next message is when I realized the machine was dead and rebooted it:
Nov 18 08:38:19 Philinux kernel: imklog 4.2.0, log source = /var/run/rsyslog/kmsg started.

Nov 18 10:29:49 Philinux pulseaudio[1825]: ratelimit.c: 229 events suppressed
Nov 18 10:56:55 Philinux kernel: imklog 4.2.0, log source = /var/run/rsyslog/kmsg started.

Nov 18 11:09:39 Philinux pulseaudio[1853]: ratelimit.c: 1 events suppressed
Nov 18 12:40:22 Philinux kernel: imklog 4.2.0, log source = /var/run/rsyslog/kmsg started.

When those freezes happened, no sound application such as Rythmbox or other was active. Sound is only used by the default system sounds (like on error, etc.).
So far, the freezes didn't happen when I was actively working on the machine (keyboard / mouse), so I suspected a relation with the power management. The machine is configured to never sleep when inactive, "Spin down hard disks" is not checked, but the display is config'd to turn off after 5 minutes.

Finally, looking at past logs, the machine doesn't always freeze after a "pulseaudio[1854]: ratelimit.c: 5 events suppressed" message, but most often, the next consecutive lines in the log indicate some severe problem: Either a reboot or some segfault (usually nautilus, sometimes a deskbar applet). The segfault or reboot might happen immediately (same second) or several minutes after the "event suppressed" message, though.

Quite often, the "events suppressed" message is followed by a "Clocksource tsc unstable":
Nov 18 08:39:17 Philinux pulseaudio[1825]: ratelimit.c: 5 events suppressed
Nov 18 08:39:25 Philinux kernel: [ 92.232052] Clocksource tsc unstable (delta = -109978147 ns)

I'm not sure this makes sense or is any useful, just trying to identify patterns...