Can't remove an arrtifact

I'm designing a plaque to be printed on a piece of wood. All looks fine in the InDesign file, but when I export it either as a PDF, as a PNG, or as a JPEG, a faint line appears across the top of the ascenders in one line of type. See the attached file. The faint line is not in the InDesign file. What do I have to do to make it go away in the exported file?