Yes. I was just going through the same thing.
Go into your Droid Settings. Go to More Settings. Then to Apps & Notifications. Then scroll down to Notifications. In there you will see Default Notification Sound. Click it and select None.
Now go back to Settings and select Sound. In there go to Notification Volume and move it all the way to the left to turn the notification sound off.
All set!
As I said in my previous reply, it is your 'notifications' sound.
If you take your mouse and click the top of your screen a status bar will appear, showing your notifications. That is what your sound is.
If you follow the directions I replied to you the other day, above, you can stop that sound. Otherwise it will do it constantly.