360 Magnum valve train noise

My 360 magnum is awesome. It made 375 hp/425 lb-ft of torque on the dyno. It has excellent oil pressure and runs smooth as a watch. No oil leaks, runs cool. I'm running FiTech TBI four barrel, it starts instantly, good response and runs great. I absolutely LOVE driving my A-body. My '67 dart has never had a better powerplant.

But, it has valve train/lifter chatter at idle. It doesn't when I accelerate, only at idle. I've read a ton of forum posts on this, apparently the 360 magnum is known to have this issue. One post said "just run 20W-50 and it'll quiet down...". I'm curious why this issue even exists. Anyone else have this issue? I'm not worried so much as annoyed. I've had Ford, Chevy and even other Chrysler small blocks with hydraulic lifters, never had this issue.

What gives?

Brian