How to disable Notification Sounds and System Sounds on an Android^™ Smartphone?

To disable system sounds 

Go to Settings > Sounds & Vibration > System Sound

Disable the following (grey out toggle by tapping on it): 

• Touch interactions  
• Dialing keypad  
• Keyboard  
• Charging  
• Screen lock/unlock  

To turn off notifications for selected applications 

Go to Settings> Apps 

• Choose the app from the list for which you want to disable notifications. 
• Tap “Notifications” 
• Select “Silent” 

Repeat for any applicable app.