Many of times users get these unwanted notification when he/she is busy on their work. Some time it makes irritate to the users.
Today I will tell you how to disable this notification sound. You will get the notification but with no sounds. This can be done is simple few steps.
Steps To Follow
1) Click on Account Settings at the right top corner of your profile.
2) Now Click on "Notifications"at the left side bar.
3) Now click on the "On Facebook" option, or click on edit option on that, under the sub menu of Notification Settings.
4) Now unchecked the the "Play a sound when each new notification is received". And click on Save Changes option.
That you are done.
Note:- This will disable all your notification sound, if in future you change you mind then just follow the same steps to enable the sound.