Pattern noise in the shadows on my Pixma Pro9000?

I did an A4 print for a client yesterday of the picture below.

In the darker areas, specifically the grey background there appear to be soem sort of noise. Extremely feint but noticable in the sunlight. It appeared to be the size of a print head, in repeating lines all down the page but only visible in the gray area.

Can anyone shed light on the subject? It's only printed about 50 sheets from new.

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Can you see it on the file of you increase the exposure? There is a massive thread on the 5D II and it's pattern noise somewhere on the board.

No, it's not there at all in the original on screen.