Lines

I will give you all the reasons I can think of.
1, If the line is only there when running through a document feeder and not there off the glass. The small strip of glass directly under the document feeder is dirty.
2. The drum has a scratch on it, or the cleaning blade is not cleaning the drum properly. Would require that cartridge replacement.
3. The fuser roller may be work in the middle. You would notice some reprinting , or ghost copying if that were bad.
4. Less likely would be some piece of fuzz in the light path, or a small piece of paper or tape in the paper path smearing the ink across the page.
If your machine prints, see if the line is on a print, if its on a print and not on the copy then it is scanner related.