I'd take a look for a bent pushrod. It can make a noise come and go. Take the valve cover off and adjust the valves and as your doing this watch the pushrods. If you have a bent one you should be able to see it while the engine is running. Look where the pushrod goes through the hole in the cylinder head, you will see it easier then. In my opinion if the spring was broken in the fuel pump the noise wouldn't go away. Might want to check and make sure the distributor is tight and not jumping up and down, but that would lead to running poor probably.
Don