This may or may not be what you are experiencing, but thought I should mention it.
I felt the same about another "dirty" roll paper. What I discovered is that when mounted in the printer, heavy paper with a springy quality can unwind enough to contact the plastic cover and other parts of the printer. I found that just cleaning the printer's plastic cover and the metal surfaces near my paper rolls completely solved the "dirty roll" problem. Have been regularly wiping those surfaces with a slightly moist t-shirt between rolls and that has almost completely eliminated the dreaded white-spot problem from all my media. I had not ever cleaned those surfaces when using RC and other thin, flacid papers that don't unwind much, and I had quite a severe build up of flaky crud everywhere in the paper that only started to matter with the heavier papers that would spring out enough to contact that stuff.