I am using slide film in a Canon EOS 1V and I recently discovered that **some** of my pictures turn out to have a **white stripe on top of the frame**, e.g. in these ones:

[![enter image description here][3]][3]   [![enter image description here][4]][4]

What I find weird is that only some pictures do have that stripe, while others turn out perfectly fine.

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 - I thought it could be the **sealing**, but taken that it occurs so
   unregularly I don't think this is the issue.
 - I also don't think it is the **shutter**, because if it was, wouldn't
   the white stripe be more parallel to the border?
 - It's also not some stain or anything from the devloping process - it
   can't be rubbed off etc.
 - The stripe shows on the slides as well, so it's not due to the scanning either.

**What could be the reason and what can I do to solve it?**

  [3]: https://i.sstatic.net/5Qzq0m.jpg
  [4]: https://i.sstatic.net/IcrvQm.jpg