[MetalMilitia]

Could be a defective line in the CCD array. Basically in a digital camera the photosensitive surface is split into a number of blocks and lines like this:

[][][][][][][][][] <- each block is sensive to light
[][][][][][][][][]
[][][][][][][][][]
[][][][][][][][][]
[][][][][][][][][]
[][][][][][][][][]

In order to read all of the data from the array into memory (for processing and eventual storage) it is necaccary to read the data off a line at a time:

[][][][][][][][][] -> data
[][][][][][][][][] -> data
[][][][][][][][][] -> data

I guess if one or several of these lines was malfunctioning in some way it would cause your images to display a line of missing information.

[][][][][][][][][] -> data
[][][][][][][][][] -> fucked
[][][][][][][][][] -> fucked
[][][][][][][][][] -> data

...or I could be talking bollocks and you just have a hair under the lens.