Could be valves. Could be something else. Try slowing down the engine by retarding the spark. If the noise goes away then the ignition is too far advanced. Or you may be able to better tell where the noise is coming from with a slower running engine.
Use a mechanic's stethoscope to determine where the noise is coming from. Or use a wooden rod held near one ear. Or use a rubber or plastic hose held near your ear. Touch the other end of the stethoscope or rod on the valve cover or other place like the cover for the cam gear. Or hold the hose near those areas.