Hey there, I recently came into posession of an automatic 87 mini ram van 2.6L. It had a lot of work done before I got ahold of it, including a new transmission about 6000 miles ago. It makes a grinding/rattling noise when idling in gear. It does not make the noise in neutral, park, or reverse, so I've just been throwing it into neutral when I come too a stop and the noise doesn't happen. It does not happen when accelerating and drives/sounds just fine otherwise. The guy I got it from says he's certain it's the timing chain, but I want to run it by a few more people before digging in there to replace it.

 

With a recent trans replacement I would check into loose Torque Converter Bolts.