I've searched , watched videos , and cant exactly find my answer . I have an 02 wrx regular EJ20 setup basically stock . I get this noise on moderate throttle . If I let off its not there . If im going into boost I cant hear it . Only when im moderately touching the throttle .You can hear it between 9 and 12 seconds . I was told piston slap is only when cold , but this sounds like it while its at operating temp .