I have a rattle from the engine today after a weekend of camping and 4wheeling. 3.7 with 223,000 miles. Regular oilchanges since ive owned it at 150k. Rattles at idle, kinda like some kind of loose metal or heat shield. And then goes away as I pick up engine rpms. Comes back around 1200 or 1500. Then I cant really hear if its still there. When you sharply let off the throttle you hear the rattle wind down... Could it be a bearing or rod knock?