Hopefully everything works OK, but here are some tips for the times when not. This section is mainly for iOS.
Apps on iOS run continuously and that can lead to a variety of issues. Most of these issues have to do with memory allocation. Just imagine having your desktop running all the time with 30 - 40 programms open at all times. Unthinkable yet on iOS we manage due to diligent coding on side of app developers. When things don't pan out there are 2 basic options to get things back to normal: Quit the app, restart the device.
Quit an app on iOS
Double tapping the home button brings up a slider containing all running apps as shown above. In that slider we can locate a specific app by horizontally drag-scrolling. Once the app we want to quit is visible just we can drag the image of the app (not the tiltle or icon) upwards. At that point there should be a brief animation completing the images path upwards, the slider re-orders now without the app. This may take a second to learn, but it is how we can quit any specific app on iOS.
When done just press the home button once to get back to the regular iOS view and re-launch the app. If this doesn't alleviate the issue, it may be a good idea to reset the device.
Restart the device
To restart your device just hold down the home button until a slider appears asking whether to power down the device. Drag the slider to power off the device and wait for one minute. Now use the power button located on the side of most ios devices to power the device back on.
This can happen in very rare occasions. Some games are extremely memory hungry and may not always release all used memory back into the pool. At that point Mozart may not be able to allocate enough memory to run its sound engine. Try the steps above in order. First quit Mozart and if that doesn't do the trick restart the device.