notification sound wont go away

Boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing. 

Hello! This sounds frustrating, I'm going to try to help you with this. Follow these steps:

1. Press the button in the top right corner, this will open up the notification center.
2. On the top, you will be able to see a "do not disturb" switch, and when you press that switch, your notification sounds will hopefully go away.

If that did not work however, you can try to:

1. Open system preferences
2. Press the "sound" icon
3. Turn down the alert volume

If none of these solutions should work, don't hesitate to ask!

Regards,

Alexander @ TechBuddy Sweden