To let you know that you've received a new message, Facebook Messenger
will notify you with a sounds or a vibration. If you wish to stop receiving this type of notification, you can easily disable
Turn Off Sounds and Vibrations in Facebook Messenger
To disable sounds and vibrations in Facebook Messenger, start by signing in. Tap Settings
and toggle the In-App Sound
and <In-App Vibrate</bolD> options to OFF
Image: © Facebook.