Add to rc.local and edit to suit your setup:
amixer set 'External Mic' mute nocap
amixer set 'Internal Mic' mute nocap
amixer set 'Docking Mic' mute nocap
amixer set 'IEC958' mute nocap
amixer set 'IEC958 Default PCM' mute nocap
This gets rid of static off when no audio is running by powering down the audio chip:
echo Y > /sys/module/snd_hda_intel/parameters/power_save_controller
echo 1 > /sys/module/snd_hda_intel/parameters/power_save
