IMM Engines 408 build

I doubt those are Comp lifters in a Magnum engine. Probably Mopar Performance, or Sealed Power, something like that since he said OEM replacements. Those usually hold up decent if the spring pressures are not rediculous, which these shouldn't be. Probably just one lifter having issues. Can you tell which cylinder, or at least which side is making noise?
Also curious why you want to change the cam? Dyno numbers looked pretty stout.