Sound suddenly gets cut off on speakers (works on headphones)

Binary package hint: pulseaudio

Sometimes, particularly when there is "a lot of loud sound" coming from the speakers, the sound suddenly gets cut off. I put the quotes to indicate that the sound cut-off is pretty unpredictable. This doesn't happen on Windows 7 on the same computer, so I don't think that it is a hardware issue.

Here's a part of messages.log (I think the last line happened when the sound got cut off):
Jul 10 15:17:30 tucuxi pulseaudio[5124]: pid.c: Stale PID file, overwriting.
Jul 10 15:22:33 tucuxi pulseaudio[5124]: ratelimit.c: 88 events suppressed
Jul 10 15:23:22 tucuxi pulseaudio[5124]: ratelimit.c: 82 events suppressed
Jul 10 15:23:58 tucuxi pulseaudio[5124]: ratelimit.c: 71 events suppressed
Jul 10 15:25:18 tucuxi pulseaudio[5124]: ratelimit.c: 64 events suppressed
Jul 10 15:26:04 tucuxi pulseaudio[5124]: ratelimit.c: 83 events suppressed
Jul 10 15:26:10 tucuxi pulseaudio[5124]: ratelimit.c: 67 events suppressed
Jul 10 15:26:57 tucuxi pulseaudio[5124]: ratelimit.c: 111 events suppressed
Jul 10 15:28:03 tucuxi pulseaudio[5124]: ratelimit.c: 66 events suppressed
Jul 10 15:40:57 tucuxi pulseaudio[5124]: ratelimit.c: 84 events suppressed

And here is part of lspci:
00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)

I have Ubuntu-supplied Linux modules for version 2.6.32-22-generic ALSA snapshots installed. I'd be happy to provide any logs after the event takes place, because it happens quite frequently.