1990 Oldsmobile 88 car noise

Tapping like a clacking sound? It most likely is a loose rocker arm. Just take the valve covers off and grab each rocker arm and see if one is loose. If none seem to feel loose lash the valves. Start the engine (just a very small amount of oil will splatter out) go over each rocker arm bolt (the bolt straight through the middle of each arm) and loosen the bolt and tighten it back down until its snug and then give another quarter turn to tighten. After all that is done and there is still a tapping, tighten each bolt a very small amount until it goes away. Don't tighten too much though. If it persists the rocker arm may have a bad bushing. Also, before lashing, loosen the arms enough to turn em to the side and pull each pushrod out one at a time and make sure that they aren't bent. Just tighten the bolt back down til snug and give a quarter turn.