Correction, it is louder though not hugely which is fine by me. The whole sound is quite different though, much deeper with a nice throb and some crackle on lift off. Remember these are not PowerFlow boxes, they are the standard BMW ones which is why I’m pleasantly surprised. Two and a half hour drive this afternoon and while cruising there was no noticeable droning or other unacceptable noises (Mrs S certainly didn’t complain). Time will tell about durability of the welds where the two systems have been connected but today I am very happy with the result.