In connection with Can an app bypass notification settings in Settings > Notifications > App notifications? (it makes no sense to copy the body of the OP), is there any configuration state other than the 6 listed there? (I found no others).
Can an app send notification sounds without a displayed notification?
As per the 6 options above, it seems it can't.
If it can, where is that set, and how can I find which apps can do that?
