Welcome to Android Central! It may be that the Chromebook's headphone jack is faulty, such that it thinks you constantly have headphones plugged in. Inspect the jack closely to see if there's any debris in there.
I can't remember off the top of my head if this is the case, but look in the notification area as well and see if there's a headphone icon. If there is, that should only be present when headphones are plugged in. If it remains after you unplug the headphones, then the jack is the problem.
08-09-2018 02:43 PM