My mothers Honda Pilot has some type of residue on the windshield. Not noticeble in the daytime, then if it rains or you wash your windshield its like little oily spots appear. You can not see if it is raining!!! I don't know what it is. Maybe acid rain?? We have tried windex, alcohol, vineagar, coke (i know that sounds strange but somebody told us to do it) I'm clueless and it's going to rain in a day or so....Please any help will be greatly appreciated.