Hello all. I have a 93 Dakota 5.2 liter with a random knock (or a thumping sound) at idle that is 2 minutes apart at times and as the engine heats up could be 5 minutes apart. When driving usually will not do it above 45 mph. Thinking either a sticking valve or a worm cam just unsure. The rocker arms and push rods look fine. Sounds seems lower. Wondering any encountered this issue? I have changed the oil (black but no shavings) and been running marvel mystery oil past 3 oil changes. Also done some carbon cleaning to see if it would clean the valves.