How to play an android notification sound

If you want a default notification sound to be played, then you can use setDefaults(int) method of NotificationCompat.Builder class:

NotificationCompat.Builder mBuilder =
        new NotificationCompat.Builder(this)
                .setSmallIcon(R.drawable.ic_notification)
                .setContentTitle(getString(R.string.app_name))
                .setContentText(someText)
                .setDefaults(Notification.DEFAULT_SOUND)
                .setAutoCancel(true);

I believe that's the easiest way to accomplish your task.

You can now do this by including the sound when building a notification rather than calling the sound separately.

//Define Notification Manager
NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

//Define sound URI
Uri soundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);

NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(getApplicationContext())
        .setSmallIcon(icon)
        .setContentTitle(title)
        .setContentText(message)
        .setSound(soundUri); //This sets the sound to play

//Display notification
notificationManager.notify(0, mBuilder.build());

If anyone's still looking for a solution to this, I found an answer at How to play ringtone/alarm sound in Android

try {
    Uri notification = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
    Ringtone r = RingtoneManager.getRingtone(getApplicationContext(), notification);
    r.play();
} catch (Exception e) {
    e.printStackTrace();
}

You can change TYPE_NOTIFICATION to TYPE_ALARM, but you'll want to keep track of your Ringtone r in order to stop playing it... say, when the user clicks a button or something.