Around the rear window, my car had some grayish looking smudges on the headliner. Neither vacuuming nor sticky tape would remove it. I was going to try a damp cloth, then I got an idea--- compressed air---sure enough, it was just dust-- air took the smudges right off like magic. Musta been dust from installation. I don't have a compressor; I just used canned air for cleaning electronics. Be careful not to spray air toward the speakers.