No, not the ADF, just the scanner glass (and not the lid...)
New clue: given your question, i just scanned something without using the ADF (just put it directly on the scanning glass and closed the lid) --> it scanned in WITHOUT the "line" - in other words, a clean scan. So it must be the ADF, right?
So how do i clean the ADF - is there a way to open it up?
OK, got it!
It ended up being a piece of the packing plastic stuck at the edge of the scanning glass - got it cleaned out, and no more line!!!