So I recently built my 4.2 and the motor went together very well. I had the best rebuilder in town do the block and spec and get the parts. The motor is tight and felt great in the process of putting it together. Me and my dad who have put lots of motors together put it all together right. All bearings in right place and pistons (motor builder assembled) are in the right hole and the machinist/engine builder did the heads. I have 2500 miles on it and it's done great until the other day I noticed a knock and it's louder cold then quiets down as it runs. I am thinking it could be a scored piston from the piston heating and expanding before the block does or a really bad pre denting (firing before piston is all the way up) I know it's not a spun rod Bering because that would get louder as it warms up. What's your opinion on this?