Hi,
I've been dealing with this issue for several months (from memory I'm pretty sure it's affected me since 2.6.36, possibly before, but I'll have to do some deeper digging to say for sure).
The problem is that the sound suddenly goes nuts and starts sounding awful. It's like some buffer pointer is just a little bit out for some reason.
I can fix the issue by closing and reopening the PCM device (as I use PA, this is just a simple "pasuspender echo" away).
The problem is very easy to reproduce - it happens about 20+ times a day to me - to the extent that I have added a panel launcher with the above fix.
We discussed this issue during the meeting but it seems not to be a PA problem (my other PA devices work fine FWIW - various USB things etc, and recording from the monitor source when the sound is odd also records good sounds).
You can hear the sounds here (recorded via mic): http://colin.guthr.ie/weird-sound/
And our discussion is here: http://colin.guthr.ie/meetings/pulseaudio-meeting/2011/pulseaudio-meeting.20...
My alsa-info is here: http://colin.guthr.ie/alsa-info.txt
This mail is really just about finding out if this is a known problem? I know others suffer from the same problem too as I've had bug reports confirming this.
Cheers
Col