1320c = Horizontal black lines every 3"

Recently my pages began printing with black/gray lines, horizontally, starting (full bleed) on the left side of the page, and getting lighter until they disappear around 4/5 of the way across the page toward the right.

All other printing on the page appears fine, whether b&w or color - and only the color black appears on the lines. No other color.

I'm attaching a picture here. It's pretty easy to see them just above the section titled "System"... Another on the near the words Paper Density -> Plain, and again at Adjust Feeder -> Coated JPN, in the "Maintenance" section.  And, of course, one additional one just at the bottom.