What process is making that sound?

Fire up the volume control which will list all applications that recently made sounds. If you have it open while the sound plays you can also see which application is doing it.

My case is likely different, but solution for me was to right-click the speaker icon on the task bar and select "Sounds". I cycled through the list until I found the sound that matched what I kept hearing. In my case it turned out to be the "fingerprint scan failed" notification and I realized I kept accidentally swiping my hand over the fingerprint scanner and triggering the sound, hahaha. But same method might help you troubleshoot your case.

I had this problem today. I changed from Windows (modified) sound to Windows default and it disappeared. Just a thought