HELP! Very Strange Black Lines

[jianglinxi]

Hello everybody,

I took some 4x5 photos in summer. I find one or two very strange line(s) on some frames.

I use tray processing to develop 4x5 negative. Beside long edge, I can see one or two bright lines (blurred) on some negatives. After I make contact printing, it shows dark blurred line on some frames. I really have no idea what is the cause of blurred strange line.

I didn't try to enlarge these frames, but I think black line(s) can be seen on large prints (11x14").

I really don't want this line(s) shows in my future frames. Please help me.

Please look at the following reference photo. I use red squares to show location of strange lines.

Thx