by doing that u are forcing all the air back through the turbo as it has nowhere to go this is called compressor surge and that is why the stock vehicle has a BOV it is bad the fluttering is the sound of air being chopped by a turbo that is slowing down. at least thats what i read my 32 has the flutter sound i installed a huge turbosmart supersonic bov when on low boost it flutters on high boost its like an air compressor exploding its great. got sounds for all occasions lol
personally i like the silver FMIC thats why I bought it and in the two years of driving coppers have only mentioned it once and i told them all turboed 32's come standard with a FMIC and they listened. (i didnt mention how big the standard is lol) but i do know you can buy black FMIC i cant think of the manufactrer but i will get back to you
i bought my entire wide body kit (bonnet,guards,front rear bar etc.) from these guys it arrived next day all in one piece with excellent quality and all fitted up. so maybe it really is luck of the draw