[JWT4700]

Hey all, so I’ve got 18k miles on new rod bearings after number 6 spun (junk yard engine) I’ve always still heard a rattle periodically but not anything consistent. Oil changes about every 2000-2500 miles so I can have consistent oil samples. I started to notice more copper in the oil filter. Oddly enough, BlackStone said the bearings seem ok and since the copper AND iron together, they think it may be valve train related. I already replaced all parts know to rattle. Where should I start with the valve train? Pull valve cover and look around? Anything specific with the cams or chains that I should look at?