After my last update of the kernel, my sound was broken. Some google-magic revealed, that there seem to be problems with the "aggressive power save" functionality on Lenovo X61s ThinkPads in the snd_hda_intel driver. The workaround is to deactivate this option.

Found here:

Subject		: snd_hda_intel 2.6.24-rc2 bug: interrupts don't always work on Lenovo X60s
Submitter	: Roland Dreier <rdreier at cisco.com>
Date		: 2007-11-08 14:55
References	: http://lkml.org/lkml/2007/11/8/255
		  http://bugzilla.kernel.org/show_bug.cgi?id=9332
Handled-By	: Takashi Iwai <tiwai at suse.de>
		  Ingo Molnar <mingo at elte.hu>
Patch		: http://lkml.org/lkml/2007/11/16/66