My MacBook Pro makes the Basso sound effect every time it wakes from sleep

Whenever I open the lid or wake my Mac from sleep, I get the Basso sound effect. It is driving me crazy. This may have started when I upgraded to High Sierra about 3 months ago. If so, it has just gotten to the point of annoyance that I didn't recognize it earlier. Otherwise, perhaps a recent OS update. Not sure. Here is what I've done to try to determine its source:

1. By process of elimination, I have fully quit each application one by one and tested until all apps were closed.
2. Suggestion of similar question on this forum (Re: my mac makes a weird noise when i open it like a space ship), went into Sys Prefs>Sound>Sound Effects tab and turned off (unchecked) Play User Interface Sound Effects and restarted computer.
3. In same discussion, another user suggested it was in Messages, and to turn off Jabber/or AIM, of which I have neither, and have also included quitting Messages in my 1st step, so that would have disabled it.
4. While in The Sound Effects tab, I noticed that my alert sound was set to Funk, and by playing each sound, discovered then that it was the Basso sound that keeps playing when the computer wakens.
5. I have some things running in the background, such as Caffeine & Roboform and have quit those to test it, but still no good.
6. So then I went to Login Items and quit, through Activity Monitor, anything that was starting up at login. That did not help.
7. Then I went through Activity Monitor to find any familiar apps that were still running and if they wouldn't quit, I force quit them. The only two that I couldn't force quit were Siri and Malwayrebytes. So I uninstalled Malwarebytes, but could not figure out how to get rid of Siri, since it won't let you uninstall it. (I have since found a website that shows how, but will try that later).
8. My last resort was to turn down my alert volume all the way, which makes the Basso tone go away, and I assume any other alert sounds.

It's got to be something running in the background, but don't know how to figure it out from here. Any help would be appreciated. Thanks!

Additional note - before posting this, I needed to Edit My Product to update it from Sierra to High Sierra. When I selected the version, 10.13.4, it also gave that annoying Basso sound!! Again, my alert sound is set to Funk, so not sure why it gave me this Basso sound when I changed my OS version. I tried to replicate it, but it would not do it again. Very strange and starting to drive me crazy! Please help!