opensuse 11.1 - USB-Headset

Some 10 minutes after reboot the sound becomes worse and stutters, volume goes down and up and it sounds like a 50 year old telephone.

Same effect with pulsaudio and esound.

Konfiguration
http://www.alsa-project.org/db/?f=08fa2abb8479e869c1dc927758a25ebf50086cde

Is there a known USB related problem?