Ticking Valve sound

After a fresh engine rebuild on a 2008 Chrysler 5.7 Hemi there has been a ticking sound like a mal adjusted solid lifter on a 1960s car .These modern engines are on hydraulic lifters that do not need adjustment .The 5.7 V8 has cylinder reduction which cuts out 4 cylinders when the engine is at light duty .This ticking noise was not present before the rebuild that was caused by overheating at 230000Km .What could it be ? Can it be fixed without too much of a pulldown? Is this issue common ?