Random intermittent alert sound on early 2015 Macbook Pro

Recently I've been getting a [super annoying] intermittent alert sound, several times per hour, on my early 2015 Macbook Pro (running macOS Mojave 10.14.4). I've gone through all my computer and various app preferences and turned off notifications, muted Chrome extensions, etc., and still it persists. When I go into the main system preferences for sounds, the alert I am getting isn't even an option in the sound effects.

I tried downloading and running SoundBunny to determine where the alert was coming from, but it seems the software hasn't been recently updated (and won't be), and I wasn't able to open the main window/menu once installed. Then I downloaded Boom 3D, which seems to think Chrome is, indeed, the source of the sound...but it doesn't get any more specific on what/where in Chrome. I'm at my wits' end...please help?!