engine rattling

Ensure the engine oil level is correct. Could the rattle you hear be a broken/cracked/damaged exhaust manifold or exhaust heat shield? It is hard to guess at a noise without being able to hear it first hand. A noise on initial start up of an engine from cold could be a sign of crankshaft bearing or piston wear problems, some times noises associated with piston wear problems may go away as the engine warms up and the piston expands, but a noise when you switch off the engine may be external to the engine like an exhaust related component.