The rattling sound a car makes can be due to loose parts or an unbalanced system. Diagnosing the problem requires pinpointing where and when the rattling occurs.
According to the Car-X website, a rattling sound in the back of the car can be a sign of loose exhaust system parts. If the rattle sounds like knocking, an incorrect fuel grade may be the culprit. If it sounds more like a tapping or clicking, the oil may be low. Another problem could be a loose timing chain. If so, the rattling is accompanied by ticking or slapping sounds at the front of the engine. The noises also get faster and louder when the engine is revved. Thumping during acceleration can indicate broken engine or transmission mounts. If a loose part is suspected, consult a mechanic.
Cars can also rattle and vibrate if the systems are unbalanced. If the car vibrates and rattles at certain speeds, the wheels and/or tires may be unbalanced, requiring a trip to the mechanic. If the sound seems to be coming through the steering wheel, it could signify worn-out wheel bearings which need to be replaced. Alternatively, the steering linkage may be worn out. A whining, rattling noise during acceleration could be a sign the cam shaft belt is unaligned or even slipping, an issue requiring a mechanic.