Why would a Dodge automatic transmission rattle when it is in drive at idle?

Answer 1

When the car is in drive at idle, the engine is running slower than if it were in neutral. The engine RPM's drop just enough for the engine to idle at a speed that creates vibrations. The cause of your rattle is probably a loose component(exhaust heat shield, torque converter cover plate, loose or worn motor mount, etc.). Rattles can be hard to find. Have someone you trust run the car in drive at idle with the brake on and walk around and check under the car to see if you can isolate it. CAUTION: exhaust pipes get hot very quickly. Use a section of hose to listen in confined areas(one end in your ear, the other pointed where you want to hear). Plastic pipe works good but an old chunk of garden hose will work as long as there are no kinks in it and it's not plugged. Sound travels very well in a tube. Once you've found the area it is coming from, you can look and feel for loose parts.(use proper safety measures) Good luck. if its less of a rattle sound and more like the car itself is shaking, it might just be low on fluid....