If you want to block notifications as well as sound then go to whatsapp settings and select notifications option. Disable all kind of notifications from there.
As per your concern, we want to inform you that if you getting the whatsapp app notification sound while using under the secure folder, you need to block the specific application notification also by using following steps.
Path: Settings> Notifications option> App notification> Select the app which notification you want to disable.
In case the issue still occurs, kindly report the problems with a log file. To share a log file, click on the Samsung Members Application (Open Samsung Members Application > Support> Tap on error report > Type your query > Send).
