When I get a notification for Snapchat or Instagram the noises won't go off?

They pop up but they never make a sound, I've looked on notifications in settings and in sounds, my phone isn't on silent (btw it is iPhone 4S) if that helps, please help it is bothering me, I tend to miss loads of notifications, it is also on full ringer, please help!

They don't have notification sounds, oddly. Same on all iPhones. Not the only 2 apps that are like this.