When fitting a Milltek pipe like one pictured (GT80) or similar twin style to a VW Golf mk4 GTI Turbo, the section shaded in brown needs to be cut off. This is a section that comes into contact with the exhaust tip and causes a knocking. This is with relation to fitting a 4motion rear bumper valance. This is because the floor is very slightly different. on the other side, you will also notice that the towing eye is also in a different place to that on the 4motion