I actually think I have something that may be similar to what you have. It's on the far left side of my screen, and is a greyish smudge about 8mm long and 2mm wide. It's only really noticeable on a black background, otherwise it just blends into the background.
My MacBook Pro, unfortunately, is no longer under warranty, so there's not much I can do, and it doesn't bother me enough.