Lines on printout when original goes through feeder

I have an OfficeJet 6500A Plus. When I run an original through the document feeder to make a copy, it makes verticle black lines, one on each side of the page. It doesn't do this when I put the original on the glass or when I print from the computer.--Only when I go through the feeder.   It's a nuisance to have to put everything on the class because I often copy multiple page documents. I have cleaned the ADF to no avail.