1. Defective Engine Mounts: Engine mounts are designed to absorb and dampen vibrations from the engine. Worn or damaged engine mounts can cause the engine to vibrate excessively, resulting in a rattling noise when the car is in gear but not in park.
2. Transmission Issues: If there's a problem with the transmission, such as worn-out gears or low transmission fluid, it can produce a rattling sound when the car is stopped but not in park.
3. Exhaust System Problems: A loose or damaged exhaust system, especially near the catalytic converter or muffler, can generate a rattling noise. This noise can be more noticeable when the car is in gear as there's increased vibration.
4. Loose Heat Shields: Heat shields protect various components from excessive heat, and they can sometimes become loose or detached. This can cause them to rattle against nearby parts when the engine is running.
5. Driveline Issues: If there are issues with the driveline components like a worn-out U-joint or a faulty driveshaft, it can create vibrations and rattling sounds. These noises may be more pronounced when the car is in gear but not in park.
6. Loose Parts or Components: Over time, bolts and other fasteners can become loose and cause parts of the car to rattle when the vehicle is in motion. A thorough inspection can identify and tighten any loose components.
7. Faulty Accessories: Some vehicles have external accessories like running boards or mudflaps that can sometimes rattle when the vehicle is in gear.
To determine the specific cause of the rattling noise, it's recommended to have a qualified mechanic inspect the vehicle and diagnose the issue accurately.
