Notification sounds mapping on Marshmallow

[AC Question]

Is there any way to find out all mappings between apps and notification sounds on Marshmallow? I apparently have several apps using the default tone, and I can't track them all down. I often get the sound and can't find anything it's signaling on the notification screen or anywhere else, and it's driving me crazy. I want to ensure all the apps have a distinct sound, so I want to see what app is associated with what sound. There must be a centralized mapping somewhere in the system, right?