Take a valve cover off, crank the engine over till both the intake and exhaust Rockers are closed...or intake closed and exhaust open and vise versa... Take the Rockers loose and watch for how much the pushrod comes up be being loose/released...then back down to compare and verify. Use your eyes and look for about .030-.060 preload but no more than .090 ita easier with the intake off.
Know that stock preload ...was up to .090 !
All share this example of an engine that we put together where the Machine Shop instead of setting the Springs up to the requirement of the manufacturer put them in really tall and they were only a t seat and around 200 to 220 open and they still never made noise like you're talking about. My own Motor stock lifters 300 thousand miles on them I put in Springs that yield 135-seat and 260 open with a stock cam and it's as quiet as it was stock. I believe if it's not the lifters 'which I doubt it's the lifters but really who knows?'.. it's the preload.
