First thing is to do like you did, check the heads for lint or a hair. Next check the cutter head as a hair can get caught on the blade and drag over the print.
If it does not look like a streak from something dragging then look at the encodor strip for dust or some stuff on it. Also blow out the area where the censor reads the strip as dust or fuzz can get in there and cause random lines in a print.
Do you see the lines when you print a test print. I am not sure on this but I don't think the test print uses the encodor scale to print it so you might not get those lines on a test print. Someone else can chime in if they know about that.