Could be your negative carrier. When you push the negatives around to align them with the opening in the neg carrier, a small burr on the carrier will scratch the negs.
Noseoil is just the oil from your skin applied to the neg where the scratch is. Rub your forefinger and thumb on the fleshy part of the skin between your nose and cheek. Your fingers pick up the oil from your skin. Rub this on the neg where the scratches are. Applied thinly, it will not appear on the print. I never remove it. I don't know what it will do to the negs in the long term. Maybe someone else does. I haven't had any trouble with negs deteriorating from the skin oils, but then I don't need to do this very often.
Hope this helps.