I also tested a clean raring by booting it in mem from a pendrive. I managed to reproduce the same unwanted effect by using google hangouts and tweaking sound levels from the "Sound settings" app below the sound icon in the systray.
I also tested a clean raring by booting it in mem from a pendrive. I managed to reproduce the same unwanted effect by using google hangouts and tweaking sound levels from the "Sound settings" app below the sound icon in the systray.