Q: iOS 9.2.1 sound on you tube and app streaming buzzing

Hey there Jerome,

If I understand correctly, there's a distorted sound issue with your iPhone 5s since updating it to the latest version of iOS. 

Try taking a look at the article linked below which provides a lot of great troubleshooting tips that will resolve most sound related issues on iOS devices.

If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support

Cheers.