Some rocker shafts tend to rotate in the housings.. and with the play between the mounting bolts and shafts, they TAP TAP TAP as they twist back and forth. It's most prominently heard between 2600-3000 rpms.
The Rockouts and Rocker Lockers ( virtually same, different companies ) take up the slack between the rocker shafts and bolts prohibiting the back and forth rotation of the shafts... no more TAP TAP TAP
I have the Rockouts waiting... I have have some stuff on order and since I am going in, I may as well install adj. P/rods.