We need more open hood videos. It honestly sounds like it could be something belt tensioner related. Just an uneducated guess.
I mean I can rev it like crazy, from 1k to 4k or above. Zero popping/knocking or strange noises. Even let it fall from 4k to 3k and rev back to 4k over and over and over. Nothing.
Plus the fact that @
fredzy's 23 does it is an interesting data point. Hopefully he can make a video for us when he has time.