70 440 stock exhaust manifolds . Loud exhaust leak on passenger side. Sounds like it's just one port. There are no scorch marks or any signs of leak. Plugs are all tight. Manifolds still tight. Defiantly coming from the passenger side head area. Took the valve cover off because it almost sounds like a bent push rod or broken rocker arm. But everything checks out. Tried using a stethoscope and still can't pinpoint it. No oil or bubbles in the coolant. I do hear a hissing sound from the passenger side if I click the motor over without starting it. No cracks in the exhaust manifold. My only thoughts at this point are a bad valve or head gasket.....Any thoughts?