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@eddieu This sounds suspiciously like a 3rd party app is causing this sound. As a troubleshooting step you can boot into safe mode. If you don't get these notification sounds while booted in safe mode, you know that a 3rd party app is causing this issue.
@eddieu This is always the difficult part. I would make a list. Delete half. Is the sound gone? If so, you know it was one that you deleted.
If not, delete some more and retest.
Once the sound quits, you can individually reinstall items from the list that you just deleted to see which one is the troublemaker.
Started disabling notifications at the individual app level
CULPRIT: Mi Fit -- my cheapie backup band to show my blood glucose was 'helpfully' notifying on every connection/disconnection....weird for sure, but not unheard of I guess.
Thanks to you and @VerbumVeritum for the troubleshooting, issues SOLVED