Hi all,
Now, I heavily use my 3880 and noticed strange marks/lines - both horizontal and vertical on prints when MANUAL REAR feeder is used (not visible with manual front and sheet feeder) as on attached scan (contrast and brightnes much exxagerated). The printhead goes left-right as for the picture. The spacing between vertical darker "lines" is ~1.6 cm and between horizontal ~2.9 cm. It appears only in dark or very places of the printout - of course not as visible as in attached scan, but clearly visible in good ligthning conditions. High resolution scan shows a bit more Y ink on darker stripes and a bit more M on brighter ones...
I tried Ilford Gold Fibre Silk, Pearl and some fine-art matt papers. Any ideas? I gave up after days of finding the reason. Increasing thicknes from 3 to 5 doesn't help.