How to track down an unwanted sound?

Windows 10 Build 14942 and Bluetooth. A four-note "attention" or "warning" sound is continually overriding my Bluetooth sound, which otherwise, seems to be behaving normally. I haven't been able to see any flashing icons or other indicators that an app wants my attention.
How should I go about tracking down the source of this disruptive sound? Is there some active listing of sound sources available?

Are you on build 14393.321? Something about Bluetooth was changed there.

I'm on 14942.1 I've turned off all sounds, but I'll wait a while and see if the update you refer to shows up. Thanks.