I did some troubleshooting and found that the sound persists in my test user account (a different sound, though), but disappears with a safe boot, so it looks like it's source is narrowed down to either a launch agent or daemon. (Does that make sense?)

I guess I"ll wait for 10.15.16 and see if I get lucky.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire