Mine was doing the same thing and I cleaned and cleaned and clean with no result. Finally I decided to gently lift up the 1/2" piece of plastic that covers the front of page scanning glass and ran my finger of all things (I had just washed and dried my hands so no oil build up) down the length of the plastic and noticed some dust had built up on my finger by doing so. This was a bit tricky because that plastic cover fits tight against the glass. THAT is what finally fixed my line issue.