lifter noise?

just went threw 15-20 mins then shut down to cool down, was running hot, 3 times... then fond out t- stat was stuck closed, and was brand new, since replaced and did 10--15 mins and revved up and held I would say @ 2500 rpms. the ach quit working, go figure... anyways, when I was doing so momentarily had a noise form passenger side sounded like lifter clacking, like collapsed. the went away. 90 psi cold, and 60 psi warm. new engine and no leaks. used com cams break in oil 10w30 and comp cams lifter break in lube, was pre primed, anyone ran into this? only on higher revs possible weak lifter? or something else? wasn't making any noise at last sun, like I said for a very brief second or two, but has done it more than once?????
318/340mp cam, old stock, not newer junk.....9.5:1 comp. 1.5 tock rockers for 302 casting heads.