Black lines on print

[NG1]

Hi

My Pro-1000 has started leaving some black lines at the leading edge of the print. I have done a nozzle clean, a roller clean and a bottom plate clean. Does anyone know what is causing this? The example in my picture is in the middle of an A4 piece of paper but there are some other much fainter smudges nearer the top i.e. to the right of those shown in this image.

Thanks

Neil