That's pretty vague. PC? Mac? Chromebook? OS version? Browser version? Could be ...

entangld · on Jan 25, 2016

Signed into FB from Chrome (version 47) from my MacBook (Mavericks).

It was 6am and I had my earbuds in and I could tell they turned on. They didn't turn off until a few minutes after I logged off.

I went to YouTube just to check. A few minutes after I closed my YouTube tab, I could hear the audio disengage.

I'm wondering if it's connected to FB autoplay videos, but those have no sound.

lsiunsuex · on Jan 25, 2016

Just did the same test and I'd say it's auto play videos.

(same setup - current Chrome / current OS X)

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.

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's not that the video doesn't have sound; it's just that the video has been muted until you click on it.

(speculation of course; I don't work for FB)