Just encountered this problem on my HD. After reading it could be a battery app, I checked, and sure enough, my battery saver had a profile that mutes the device when the battery is low. Problem is, the HD was fully charged! Worse, I couldn't uncheck mute on the profile. So I created a new profile with no mute, applied it, and sound came back! App is Battery Doctor. I think lt's a good app, but you just have to be careful about the profile.
2 weeks ago - last edited 2 weeks ago
This happened to my HD just today. I couldn't figure out what was wrong and even rebooted it. But I promptly googled the issue and came up with this thread. The solution to download and use Volume Control+ worked perfectly. Thanks to those who posted the answer. I was bummed out for awhile thinking I might have to send it in for repair under warranty.
I also have Battery Doctor installed. But my battery never fell below 50% today. I don't know if that app was the cause, but just to be safe, I uninstalled it. I wasn't using it anyway. I use Greenify and App Killer to monitor and manage battery drain. I also use Llama, which is great for automatically shutting off Wi-Fi when the screen goes off. I found that made a big difference in battery life.
So thanks again to all for this helpful thread.