Volume being set to 0 by a ghost?

I normally have my volume set to 3 bars, I never for any reason mess with it. If anything I use the mute slider. But since I installed iOS 9, I sometimes find my volume is at 0 bars. Mainly when I am opening games (Simpsons Tapped Out and Clash of Clans). Anyone know why this is happening?

 

Figured it out from an Apple forum. Whatsapp is muting it when you go to the camera app within it. Apparently for Snapchat too.