My Epson Stylus Pro 9880 is printing fine on paper (the weightiest being 315gsm). Until recently canvas printing has been good (360gsm) but on a recent batch of large prints (A1 & A0) there are what appear to be faint "scratch" marks occurring randomly. There is nothing apparent that could be causing this. I've also made sure that the prints are being carefully caught and placed on a flat surface at the end of the printing process. Does anyone have any ideas what may be causing this?