poor oil pump, low oil pressure. Did you change all the gaskets on the top end, e.g. cam seal, maybe try re-lapping the valves etc... all cvh's are noisey, my sounds loud but im using double valve springs and anti-pump lifters.

also you need to change the tappet\lifters at the same time when changing the cam otherwise the tappets will wear funnny and vice versa with the cam.

Ive known people just change the tappets on an old cam and within 20 miles there noisy again becase they've warn to the old cam!