Im not sure about Snap Chat but for Instagram the sound is off by default. You have to touch the little equalizer in the upper right corner of the video for the sound to play. They have it off by default for privacy reasons people were complaining cause they didnt wanna be in a store and be scrolling through and stop at a video and have the sound just start playing. Not sure if that helps or not. If it doesnt then it might be your speaker thats the problem.