Loud banging coming from intake area

Replacing head gaskets in my mother in law's car. I put the car all back together and then realized I hadn't tightened the rocker arms on the rear head after I had started the engine. I know I heard a really loud banging sound coming from the upper intake plenum. I shut the car off removed everything got to the rocker arms pulled them out took out the pushrods check the pushrods and they were all straight, so I put it all back together and started the engine again and still heard the same loud banging. I really need to know what this could be what I could have damaged and how to fix it. Also I cleaned out what I thought was a port to the egr valve in the upper plenum. It looked as though it had become plugged with old oil and carbon. This port comes just behind the opening to the throttle body to where the egr is mounted. Could this be causing causing the hammer on metal sound I can hear and feel?