Mine 5.0 is quiet unlike both 04 mach1's I had after they came up to temp had a tick. Did it hurt the engine NO wasn't nice to hear but it never change in sound. Tolerance stacking of block, head, valvetrain when everything is put together. Exh leak can sound like valvetrain noise. Have seen injectors make a lot of noise before. I do think it's from head cyl after it warms up because being alum it expands. I know from machining alum it may measure out right come back next day blank blank would change. Must machine slowly and keep it flooded with coolant/cutting fluid.