I have develpoed a knock in the right side of my engine (looking in hood). It is really faint when I first start it, but as soon as I step on the gas it gets louder and faster. When the engine gets HOT it knocks harder too. I thought it might be a lifter or a bent rod, but I checked them both and I checked the springs and nothing was wrong. I was going to take the oil pan off and clean it out and replace the pump, and while I was there look around in there, but I can't do that without taking half of the stuff out from under the truck. Inside the valve covers was filthy and it looks like the guy who owned this truck before me didn't change the oil regularly. Could I just have one of my valves blocked open by crud and it be fixed with a good engine flush from good ol' Auto Zone or could it be something very serious that will take ripping the engine apart? It isn't missing or back firing, and it seems to be running normally for an old pickup. Please give me ideas.