I was told years ago the fuel was added on decel.... to cool down the cats a bit after doing a wot pull etc. The unburnt fuel gets burnt up in the blazing hot cats anyway, causing all the racket, so duno if adding fuel is doing anything in the way of cooling down the cats, or anything else. If coasting for a bit in drive, ( 4th).. then manually shift down to 3rd or even 2nd gear, I don't get the racket. But if I give it a bit of gas after coasting 1st, then downshift, then I get the racket, so at least it's controllable. IE: wind it up a bit in 3rd gear, then drop it into 2nd gear.. right at a bus shelter, then scare the shit outa everyone standing there waiting for the next bus. I do that to, if I see that a cop has a ricer pulled over. Then quickly turn the corner so they can't get ur plate number.