Mine is a longlife exhaust, same as powerflow. 2 ways you could fix this. First take and back and get the garage to change it. Secondly you could get some sound proofing and line the boot with it. Car will still be noisey but not as loud inside the car
Pic of mine


Video
http://www.filecrunch.com/file/~aeo501 right click, save as when it says down load ready.

Mine is very loud all the time, Just turn the music up