I have a 1994 pontiac grand am v6. It has 43,000 miles on it. I just changed the head gasket and new pushrods. But when I turn on the car. It started to knock but it knocks louder when I put it in reverse. The pushrods are in order. Intake are the short ones. And the Exhaust are the long ones. I place them in the right order but it still knocks pretty hard once I put it in gear. But louder in reverse. Any Suggestions on what it could be?