YouTube app volume sounds extremely low

I've noticed that I've been having some sound issue with my iPhone 5s, mostly with the YouTube app. When playing videos, it sounds as if the volume is turned down low even though the volume is at max. The video sounds seems to go back to normal when I receive another app notification and pings and then the volume seems to correct itself while the video is playing until I exit out of YouTube or go to another video. Any advice would be much appreciated.