My buddys 95 Trans am has been sitting for a year and he started his car and has this knock. The car never had the problem before and thier was definitly nothing wrong with the motor and you can not feel the knock on the valve cover or on the manifold. After the car warms up the knock gets quiet and almost goes away. Also the car does take about 8 seconds to start while the key is held. The opti spark is my best guess and I just wanted to check with more people if they had any idea