Hi i have a 1999 dodge durango and it makes a wierd sound at back of motor by trans sounds like something rattling just started couple weeks ago funny thing is it only does it while in park once you put it in gear it stops what could it be

Cud hav a loose linkage that operates shifting-the idling motor causing vibration--youll need to get some info at library or online for ajustment procedure

I would check to see if there is a heat shield, or protective shield in the area that you described, that might be loose or need tightening up, this could be the vibrating or rattling , when the engine is in park, due to the higher rpm's, also check to see if transmission mounts are tight.