Who I have the same questioned this topic

android moto Z phone. vibration motor works but has started to make a metallic rattle when it activates, as if it were loose or is rattling something inside the case. the short-press buttons (back, home, apps) do not make the rattle but any other longer vibration does (including vibration test apps like 'vibration plus'). the phone was not dropped, did not get wet, and is intact in terms of abuse of other sorts. It has an otterbox dual-layer protector, and makes the rattling sound regardless of if that is on or not.