Modern engines all have knock detection sensors that will retard engine ignition timing if they detect ping. You would definitely get a check engine light if this sensor was malfunctioning too. The fact that it's repeatable at a specific RPM makes me think the problem might be an under hood component that is vibrating and sensitive to the harmonics present at that specific RPM. Possibly something that is routed incorrectly or missing a clamp meant to secure it and is touching another part that it is not supposed to be touching. These kinds of issues can be difficult to locate. Best of luck with it.