Hi sollekram,

A little late reply, but maybe it still helps you out.

You might want to take a look at this github issue: No sound while i got new notifications and maybe you will find a solution for your problem there.

This module is only using the access token to communicate with the PushBullet API. This module and configuration is running on your Magic Mirror which is not publicly accessible.
If your PushBullet access token is compromised someone can pull your notifications, if you think this is the case hit the button ‘Reset All Access Tokens’ on the PushBullet website (https://www.pushbullet.com/#settings) after login and create a new access token.

Bas