i had a new back box fitted about a week ago, but now i've noticed its gone black inside the tip like black dust/powder type thing, is it normal for it to go black inside, or is there something wrong with my system before it reaches the back box, i'll get a pic in the morning, thanks for any help

mines black inside

Same with my Punto. You wanna see the dirty diesel's exhaust that ive got now though........!!

thanks guys, i was worried, thaught something was up with it

This is normal with exhaust that have a cat even if you drive it as hard as one can.