5.2 Magnum Question

If the lifter makes noise and the preload is right you may very well have a bad or weak lifter, but then again hydraulic lifters rely on oil supply and I can't say that my Magnum has ever been down around 30lbs so it makes me wonder if it's a lifter or oil supply to it.
IF I was using a 30+ weight oil already I would pull that lifter and replace it just to see what it does.
If not using a 30+ weight oil I would first try something a bit thicker and see how it acts with that.
Obviously you want to look the rocker assy over for wear as well. (this could show as not enough preload)

Just what I would do, so...