My iphone wont make any noise?

For some reason my iphone wont make any noise. When I take pictures, my I get call.... so when someone calls me I have no idea! It's really annoying. I looked in Settings>Sounds> and the ringer volume is up all the way, and all the other sound options or in the ON position, so wtf! Is it a malfunction? The only time i can get it to make noise if I have an app open or I'm watching Youtube on it...