Just check there the exhaust pipe connects to the exhaust manifold. On each side there is a "donut" type gasket that is used for the seal. These are known to work loose and rattle. It is a simple and cheap fix IF you can get the bolts loose without breaking them. If you see any movement at this joint, spray penetrating oil on the bolts and let them sit overnight. Then you slowly try to get the bolts loose by turning them in each direction until they break free. Use more penetrating oil as needed. The gaskets should be available at any auto parts store.
