I want to switch off the update or comment tone in FB. I get the beep sound, when any of my friends comments on an update that I have commented on or I am following. It is just irritating.
Click the gear in the upper right corner of the window and go to Account Settings, Notifications, How You Get Notifications - On Facebook - View, and uncheck Play a sound when each new notification is received. Then click Save Changes.
See also Facebook Help.