Illustrator doc's opacity mask/photo images print with lines, why?

Some of the hi-res photos I've used w/ opacity masks in Adobe Illustrator print with dark lines through them. The pix are 300dpi. The lines do not appear on the screen.

I've tried rotating the images or moving them slightly and this sometimes helps, but is not the fix I'm looking for.

Could this be our printer? We have new ink cartridges and have cleaned the heads, but this doesn't appear to help either.
 
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