Looks like something in your developing tank is scratching the negative. When that happens, the scratch is clear, and it prints black. It's such a straight and thin line that I can't think of anything else it might be, particularly as it is consistent with other developed rolls of film. It won't show up in the rebate, of course since the rebate between negs is clear, but if it traverses the whole roll, it's a scratch for sure. What tank do you use?