If you are experiencing issues with sound quality, volume, distortion etc and you are running Android 5.x Lollipop please try disabling 'Nuplayer' from the developer settings. This is an experimental player Google introduced to Android and is known to cause some issues.

To disable open up the settings app from your app drawer. Scroll to the bottom and tap 'About'. Find the 'Build number' detail (possibly in 'Software information - More) and then tap on the build number 7 times until it flashes "You are now a developer".

Now go back to the settings screen and above where you tapped 'About' you should now see 'Developer Options'.

Tap this and scroll down until you see 'nuplayer', if it is checked uncheck it, go back to your homescreen and restart your devce. Hopefully the issues you had should be gone.