99 times out of 100, the problem is flaking, wherein a tiny speck of a paper's inkjet coating pops off the page after printing, leaving a glaringly obvious white spot. This is most obvious in dark areas of the print, of course. As others note, brushing off the paper before printing helps a great deal.
In my humble experience these defects are generally tiny, and can be rendered invisible by touching them up with an appropriately colored speck of ink. I have a couple of pigment ink pens I've used for this. If it's a print I'm selling, I'll bite the bullet and reprint it unless the defect can be eliminated with a single touch of a pen. If it's a print for my own use, I'll happily mix up a tiny dab of acrylic paint in a matching color and paint it out.