I was out running my car tonight and I got it too about 5000rpms in third gear when something let loose. It sounds like something is hitting the valve cover on the passengers side. I took off the upper intake but I was to tired to go any farther. When I turned the motor over the last cylinder on the passengers side was blowing back through the lower intake runner and making a popping sound. I have scorpion rocker arms on afr heads. Does it sound like maybe one of the rocker arms somehow loosened up on me. The way it is blowing back through the intake makes me think that the exhaust valve is not opening for some reason.