Bug #464442 may be related. At least the workaround in https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/464442/comments/11 worked to fix this bug for me.
Bug #464442 may be related. At least the workaround in https:/ /bugs.launchpad .net/ubuntu/ +source/ alsa-driver/ +bug/464442/ comments/ 11 worked to fix this bug for me.