Note: If you want to play a sound for a long time, you will need to loop it. The Sound component does not have this capability, but the Player component does.
However, since Android 6 the Player component can no longer loop seamlessly (gapless). You should therefore use the TaifunPlayer extension App Inventor Extensions: Audio Player | Pura Vida Apps. You also need to use OGG as the audio format, since the MP3 format is basically not loop-able.