rod bearing means removing the oil pan, which means pretty much pulling the engine or if you have a lift removing most of the underside. Is it a deep knocking or a rapping noise? need to be more specific on the noise. the valve cover holds many parts that can be fixed easy and make a rapping tapping noise. Lifters, rocker arms...valves. Rod bearing would be deep in the engine knocking about the oil pan area. any noise like that can damage an engine, I wouldnt drive it unless you really really have to...just my opinion.