Just did the same test and I&#x27;d say it&#x27;s auto play videos.<p>(same setup - current Chrome &#x2F; current OS X)<p>I turned on auto play videos, killed the browser, waited for my headphones to turn off and went back into FB - scrolled down and when a video came into view, the headphones turned on.<p>Even though the video might have no sound, the html 5 video element still needs to allow sound to pass through. When videos auto play without side, it&#x27;s not that the video doesn&#x27;t have sound; it&#x27;s just that the video has been muted until you click on it.<p>(speculation of course; I don&#x27;t work for FB)