that statement makes no sense. rod knock means one or more of your rods are banging(knocking) against something. so when you say you bought a new one what did you buy?
and dont think where its coming from stick your head in there and listen. first put your ear just above the valve cover, see if its there. then go under the car and listen. where ever its louder that is usually where its at. does the knocking get faster as you rev?