[Siciliano611]

I bought my 09' m3 in January and the previous owner had a Magnaflow axleback exhaust installed, which i like the design and sound, but what I notice is I can clean the inside of the tips with grime reaper (chemical guys) and steel wool, and it will look amazing and shiny on the inside, but just 3-4 days later they are black on the inside again...Does the m3 engine run very rich and hence all the soot already on/in the exhaust tips? It is annoying cleaning the tips as often as it seems I have to