I have the same problem. Stuttering sound when browsing with Firefox or Chrome, in Firefox it seems a bit more severe.
I found out about DPC Latency Checker, which you can find here: DPC Latency Checker
Run it, browse, and if you see red spikes, something is wrong with one of your drivers
. It's somehow interfering with your CPU causing the distorted sound.
Then try to deactivate devices in device manager one by one to see which one is the cause.
In my case it was Norton Internet security 2011! I uninstalled it and alle the hickups and red spikes are gone. Sound playing nice. Now going for Kaspersky 2012 which does not seem to have this issue.