TURN OFF FACEBOOK'S NOTIFICATION SOUNDS
Tired of having Facebook notify you every time someone likes a post that you've made? You can turn off Facebook's notification sounds.
Click the upside down triangle in the upper right-hand corner of the Facebook page, then click the "Settings" link. In the left column select Notifications.
Where it says "On Facebook," click the "View" link and uncheck "Play a sound." Then click the "Save Changes" button.