Confirm it happens through the document feeder and off the platen glass and it would imply heavily a hardware failure or the scan light itself. But in the case of the light, it would have to be an issue for copies and scans. And for the hardware it should be all scans, not some. Try eliminating the hardware by scanning as TIFF, if it still happens it will be the glass.
The more likely scenario by far is that it would be ADF only, and in that case it will be something on the small strip of glass to the left of the platen.
If you come back and attach a pdf I may possibly be able to troubleshoot that further, but experience points to something on that strip of glass.
Perfectly straight lines that show up across the page in the same direction it travels through the feeder will absolutely be on that strip of glass, try a rag for the light easily removed stuff and the edge of a credit card for the other stuff like whiteout from a previous job run when it was still not quite dry.