After installing Ubuntu Mate 16.04 I encountered a strange feedback type noise when I plugged in my headphones. The noise would stop when I open the sound settings, or when I played audio files. The noise would start again when I closed sound settings and/or stopped playing audio files.
What I discovered was by default the audio power saving feature that ships with Ubuntu will put the sound card to sleep when it is installed on a laptop, and the laptop is running on battery power. When the sound card is asleep the feedback type noise is heard in the headphones.
The work around I used was to disable the audio power saving feature as follows.
Open the Terminal and run the following command:
gksu pluma /etc/default/tlp
Find the following section in tlp
# Enable audio power saving for Intel HDA, AC97 devices (timeout in secs).
# A value of 0 disables, >=1 enables power save.
SOUND_POWER_SAVE_ON_AC=0
SOUND_POWER_SAVE_ON_BAT=1
and change it to
# Enable audio power saving for Intel HDA, AC97 devices (timeout in secs).
# A value of 0 disables, >=1 enables power save.
SOUND_POWER_SAVE_ON_AC=0
SOUND_POWER_SAVE_ON_BAT=0
Save and close the file.
Then reboot to take affect.
This ended any abnormal sounds when the headphones where plugged in.