worked at a shop were this mustang had a new ford crate engine and a new tremec trans. ran but the guy had this sound that went rigth thru the trans . sounded like it was getting hit with a hammer .so i looked at it for him he was thinking it was the trans but he had the wrong fireing order. the give away cold tub on the header and it really did not sound like it had a dead hole.you can check were the sound is coming from with a broom handle the type that unscrew or a very long screw driver