@twaelti: If you was replying to me - it's as Manuel says: Nothing playing, so no reason for pulseaudio to be active at all (well it's running all the time, but it should be _idle_, as it normally is when there's no application using sound).

In the meantime I have looked at all active processes and found nothing that should trigger this. So I killed pulseaudio, it then restarted (as it should), but now in idle mode, no CPU misbehaviour. There's something wrong here.