Problem with A3 convertible roof fabric
 

Hi
I got this problem with my A3 convertible roof .
I have a lot of triangular shaped stains on the back of the roof, on the sides next to the rear window.
It is definitely caused by the roof folding in to the back, leaving these triangular fold-stains. The top is black; the stains have a grayish appearance. They don't go away with regular washing.
Anyone knows what could be causing this, and what I could do to get rid of the stains?
Thanks for any help....