A sample would have helped but here are some questions/tips.
- does the defect show up on scans from the document feeder and the glass or just document feeder. Most common issue with lines on scans is debris on the glass. The ADF scans using the small slit of glass to the left of the main glass. Look closely, due to the way that scanners work, they will cause a defect from even items like a tiny spec that you cannot really notice.
Use caution as many of the smaller HP units have a thin mylar over the ADF glass to ensure that pages do not jam and if you damage or remove it you will create more problems for yourself.
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