Recently got a 2021 explorer ST in the beginning of April. The build date is 10/2020 and I am hearing a knocking noise only under load coming from the engine. It was in the shop for 2 and a half weeks, and their conclusion was that it was a normal sound. I am not so easily convinced as I know what "normal" valve train noise is... This noise happens whether it is warm or cold. It only happens under load, I cannot hear it when parked.