I have a 1991 Chrysler New Yorker Salon only 39,000 miles V-6
When I am in a drive thru- for example at the bank - and I am stopped - but leave it in drive - I hear a loud rattle. However, if I shift into Neutral or Park - while I'm waiting - the rattle goes away. When the car is moving - the rattle goes away.
Not logical, There would be constant pressure keeping a loose joint tight when it is in gear. Would you describe this a tinny rattle. If so there is probably a heat sheild loose over the converter. Tap the exhaust with a rubber mallet and you may be able to track it down.