they are probably acid rain spots. I would suggest going to a car wash that has a detail bay and have them buff the windows to get it off and then sealed to help prevent them from coming back. I work at one so i know they can be removed in about an hour for all the windows so you should be looking around $35-45 to get it done. You might ba able to find a product and do it yourself but i would just sacrfice the $45 and save your elbow. Hope this helps. Blake