In Lollipop and below, you could easily send a sound only notification by omitting the icon, content title and content text when constructing, like so:
NotificationCompat.Builder builder = new NotificationCompat.Builder(getApplicationContext());
builder.setSound(Uri.parse(ringtone));
notificationManager.notify(9998, builder.build());
In Marshmallow, I'm forced to include at least an icon, or I get a 'no valid small icon' exception. I want to use the Notification system, but don't always want to display a notification in the notification bar. Is this possible with Marshmallow, or should I change to playing my notification sound with media player, even though sometimes I, or the user, may want to display a notification?