Okay: There are other things you can do.
Use File Explorer to search for the .wav files - especially those that are used by windows.
Start at C: drive and use "Win*.wav" (without quotes) to find sound files. Unfortunately you may need to click through all of the sound files to find out which file generates the sound and then use the file name to further track down possible reasons.
There may be some help available in another way.
Look in Reliability History and Event Viewer for error codes, warnings, and even informational events that are captured at the times you hear the sound.
Run as Admin.
Because you are not seeing any pop-up windows with error codes and warnings, my thought is that the sound is probably being generated by some informational event. No guarantee about that - so do look at error codes and warnings anyway.
Reliability History uses a time line format. Much more user friendly. Just keep Reliability History running and minimized. The next time you hear the sound, open the window and look for new entries. You can use the same method with Event Viewer - just not as easy to navigate and understand.
Starting point in Event Viewer = Windows Logs > System. Again you will probably need to look at the other choices as well.