How can I know which app is giving me notification sounds? I've removed the permission for almost every app to show me notifications on the status bar but now that led me to a situation in that a lot of times during the day there will be a notification sound (which in my case is an annoyingly loud "boom", which I use because that's the only way I can hear the Redy Gym Log notification that my rest time is up with the loud sound in the gym) but I don't know from which app it came from. Is there any way for me to turn off sound notification? I can't find that on App Opps. Maybe an app that would show a behind the scenes system log would be great, if that kind of thing exists. I'm on a Galaxy Note 3.
For system logs you have the "logcat" command. 

you culd try killing apps one by one untill you find the naughty one. But unchecking notifications should work, so are you sure you disabled almost all? It's probably an app that is still notification enabled