You can mange your notification sound settings by right-clicking the Start menu and selecting "Settings".
From there, choose "System" then "Notifications".
Make sure you turn Notifications On (if they aren't already) then click the small arrow next to the On/Off slider. This will give you access to more specific notification settings, ensure that "Allow notifications to play sounds" is checked along with any other notification settings you need.
Afterwards, scroll down this page to find your web browser and click it to open advanced settings. Make sure "Notifications" and "Play a sound when a notification arrives" are "On" as well as setting the priority of notifications to Top.