Whenever I open the D365 UI in the browser, I'm greeted with a small bell sound. This is caused by supposedly unread messages (the little bell icon in the top right). Unfortunately, you have to delete the messages to get rid of the bell sound (at least until the next message is added).

The D365 UI should honor the Windows settings for sounds. If I select schema "No Sounds", it should not play a sound, even if I have messages.