Windows 10: Unwanted repeating xylophone sound, how to turn off?

I have a repeating periodic xylophone type sound that my computer keeps making. It's annoying and I can't seem to figure out how to turn it off. It doesn't seem to be associated with any particular program. The "Adjust System Volume" has the speakers on (so I can listen to music or videos) but the system sounds are turned off. Notifications are turned of. System sounds are set to "none". Any ideas?

:)

 

why notification sounds changes when phone is on a tilted surface?

I got a Lumia 920.

When I leave the phone resting on a tilted surface (or wherever it lays in a not horizontal position), the notifications sounds are added with a second sound that is like xylophone arpeggio or something like that. When I pick up the phone, it gets its
usual notifications sounds.

It is a repeatable behavior but I wasn't able to find an explanation.

Thanks in advance for your help!

 

A turn-on sound in new N-Gage

I've been hunting for an option too, to no avail. I've got the games on mute for the bus and still there's this rampaging xylophone sound jumping out at me.

 

Could be some malware, I don't recall any such system sounds.

 

After some trial and error, I figured out it was one of the programs. ITunes isn't playing well with my system. I now use the windows music app "Groove Music". No problems and it sounds better?