Vibration noise

A common cause of this type of noise is a loose exhaust heat shield. You will have to have the vehicle on a hoist, or jacked up, with jack stands, high enough so you can crawl underneath. Gently attack the various shields with a rubber hammer. Some shields are bolted to the body, above the exhaust pipes and catalytic converter. Look for holes corroded around those attaching nuts that let the shield droop. Some shields are welded to the exhaust parts, and those welds can break loose. Most commonly heat shields on exhaust parts rattle from engine vibration, and that can be engine speed-sensitive. Shields on the body are more likely to rattle from things that shake the body, like pot holes and bumpy roads.