Car speaker rattles/vibrates?

OK so i have a 2001 oldsmobile intrigue with 35k miles....so its not used that much its just kind of old. But anyway the front passenger door speaker rattles when there is bass. It is rather loud and annoying and flicking off the speaker doesn't help much at all. so does anyone know what could be causing this cause it is very annoying and i would like it to be fixed. If anyone has any ideas or ways to fix/ buy stuff to fix this i would be very grateful. Thanks for your time society.