Sounds like it but not too sure exactly. When idling, you cant hear it, but once moving it starts to knock slowly, and increases with speed. Sounds like its coming from under the rocker covers or that area, and its close to the drivers end than the front. I assume its an exhaust valve loose or something, but before i get it checked out for sure, does anyone know if im correct, or could this be something else. Also, should i stop driving my car incase this could lead to bigger problems. Previous owner said something about fixing a valve problem with him. Would this be expensive to sort out? Any suggestions on better valves to use if needing replacement.