Comment 5 for bug 75906

After some experimenting, I have a few ideas about what might be going on, and a workaround.

The best test for this bug, in my opinion, is, while using headphones, to play the test sine-wave from within System > Preferences > Sound (the "Test" button under, say, "Sound Events"). It will be very clear whether the left channel distortion is present.

I've found a work-around that works reliably on my MacBook Core Duo (not 2).

1) In System > Administration > Login Window, on the Security tab, enable automatic login to your user.

2) In System > Preferences > Sound, on the Sounds tab, uncheck "Play system sounds".

3) Reboot and test as mentioned above.

Can anyone else confirm that this works?

I'm using Feisty with all the most recent packages at this time, kernel version 2.6.20-12.

I believe some kind of race condition is occurring such that if a sound is played before the driver finishes initializing, the sound chipset gets into some broken state.

There is related forums thread here:
http://ubuntuforums.org/showthread.php?p=2317339