Why does my Pontiac Boneville make a rattling noise only when I turn it on

Hello, can you tell where the rattle is originating from? Engine area? Suspension? Exhaust? Rattling could be internal or external exhaust components making noise which can indicate a small or big problem. Engine noise can be from a major internal component or it could be from a tensioner pulley for a belt or similar component. Too hard to tell without ears / hands on testing.