Red light from headphone jack Macbook Pro running Ubuntu 14.04

I'm getting a red light from the audio jack on a 2012 Macbook Pro. I'm running Ubuntu 14.04. Sound works fine, headphones or speakers, but whenever the sound is on the light comes on. It usually turns off when the sound does (but not always, or immediately)

I'm using ubuntu-16.04 and after so many attempts I figured out the solution.

These are the steps to solve red light audio jack issue in Macbook.

1. open system settings.
2. go to output tab, select speakers - Built-in Audio option under Play sound through category.
3. look for the mode option under settings for speakers category.
4. Change mode from Analog Stereo Output to Analog Surround 2.1 Output or Analog Surround 4.1 Output.

Enjoy!