Quiet your engine by tightening the rocker arm to cylinder head end play clearance. FEULING recommends an ideal side clearance of 0.035 - 0.005 for optimum rocker arm oil psi and noise reduction. M-Eight cylinder heads also have excessive wear on the rocker arm standoff trusting surfaces, when the hardened shim is placed on the thrusting side it will assist in reduction with further wear and damage to cylinder head.