Cam and lifter problem

I think the Comp lifters have that bleed down valve like the Rhoads lifters and maybe when the oil gets hot and thins out it rattles.
I remember when I had my 454, it had Rhoads lifters in it and they did make noise. But I never had any experience with Comp lifters so I'm just guessing. You could try a anti pump up lifter since you have a adjustable valvetrain.
Bob