For God sake people stop panicking - it's force touch trackpad that is causing this rattle. Loose elements which vibrate when you touch it...
https://forums.macrumors.com/threads/omg-try-to-shake-your-macbook-pro-2015.1985964/page-2
https://forums.macrumors.com/threads/omg-try-to-shake-your-macbook-pro-2015.1985964/page-2