This problem presented itself upon upgrading to ubuntu 9.10.
Any time something affects the sound system the buzz goes away. If a song plays, no buzz. If I simply adjust or mute the volume, no buzz. But after 10 seconds of no sound related activity, the buzz returns. This is a very loud and aggravating buzz, most likely made worse by the fact that I run my sound through an amplifier.

This feels like something I should have been able to easily find an answer for, but my search terms must be whack because I can't figure it out.

Thanks

Hi odocoileus, Welcome to LQ. Take a look at your mixer and see if your mic boost is turned up.

Good luck. ;-)

I finally found it!

in /etc/modprobe.d/alsa-base.conf

there is this line:

Changing the 10 to a zero and rebooting fixed my problem.