You can toggle both game music and sounds on/off in the game's Settings menu. Tap on the cogwheel icon in the top right corner of the main screen to access the Settings menu. 

• Tap on the Music Note icon to toggle game music on/off. Tap it again to change your preference. Disabling game music will not disable game sounds.
• Tap on the Speaker icon to toggle game sounds on/off. Tap it again to change your preference. Disabling game sounds will not disable game music.

The overall volume of both game music and game sounds is the same as the volume of your mobile device.