Just a thought ere,you said you installed hiperf heads.

well a few things come to mind here that can increase valvetrain noise are as follows:

* If heads have higher spring rates then stock heads did which is very likely that can cuase the valve to hit the seats harder which will increase valvetrain noise.

* If you installed a higher perf cam with more gressive lobe design that also increases vlavetrain noise even with hyd lifters.

* Another issue could be the bleed rate of the replcement automotive lifters could be slightly faster or the machining quality be lower causing same issue with respect the plunger and lifter bore tollerance causing them to e noisier too.

Or if your new high perf heads do have stiffer springs that can cuase the stock perf automtive hyd lifters to bleed down a little faster/more then they should too addition to valvetrain noise too even if still runnking the stock cams.

* Are you running a lighter oil like 10w-40 or 15-40 vs 20-50 and if yes try some heavier 20-50 or race oil in 25-50 or 20-60 grade to see if that helps some if all other things like valve adj etc are checked again and are ok.

I have been working on and building SBC/BBC street perf motors for over 38yrs and often run into issue with increased valvtrain noise from hi perf hyd flat tappet cams bothering the car owners after those hi perf cams with more agressive lobe designs are installed,its just part of the drill with perf cams having agreesive lobe design allown vlaves to seat faster & harder esp with the higher sping rates required with those cams too.

Scott