Magnum Head Rocker Arms

It's probably the lifter preload... Magnum rollers aren't like your typical flat-tappet hydraulics, they like .080"+ preload or they will be noisy. I have a 150k+ mile 5.9L Magnum short block with stock lifters and stock LA rockers (long story) on a custom-grind Racer Brown cam and the valvetrain is not much louder than stock. It's got at least 15k miles on it since I put it in my Duster. Had to get custom-length pushrods when I put it together to get the right lifter preload.