Light Grid of Dots of Printing Lightroom

I have a printing problem with several images -- there is a light, barely discernable, square grid pattern of small black dots on the prints.  On one print the grid lines are about 3/8" apart and on another about 5/8", both on 8 x 12" images.  The images are TIFs that I created by exporting them to Photoshop for some work and then back to Lightroom.  However, when I print the same images in Photoshop there is no grid.  This does not happen with all my Lightroom to Photoshop and back TIFs.  I have no idea what might be going on. I using a Canon Pixma 100 printer in color. I can't see the grids in Lightroom (or Photoshop), but they show up on the Pixma preview screen.