There is a loud rattle coming from underneath near the automatic transmission area of my old '97 Dakota 2x4, 3.9, which I sold to my father-in-law a few years ago. It only makes the rattle when in drive, reverse, or a low gear and it is very loud. It makes this noise when in gear and NOT moving. It is completely quiet in neutral and park. It sounds like a rock banging around inside the catalytic converter. It is not rhythmic. The truck drives fine and the transmission shifts smoothly down the road. Other than the noise there seems to be nothing wrong.


Any ideas?

 

Some heat shield somewhere, or a rock stuck between the heat shield and converter.