Comment 8 for bug 466936

Hmm, just changed sound with alsamixer -Dhw:0 Master slider a bit and now the distortion disappered... it's now as clean as with speaker-test -Dsurround51.

Somebody on ubuntuforums.org wrote that you can reproduce the distortion if you touch the fade or subwoofer slider on the output tab in the sound preferences dialogue. I confirm this behaviour. If I move the sliders back into their original position, the noise disappears again.

forum post: http://ubuntuforums.org/showpost.php?p=8290572&postcount=13