My desktop has been displaying stripes, once when it crashed and the second time while it is tiling photos on my desktop, is this normal?

I have some screen grabs that I'm using for my desktop. Some are small, but some are almost as big as the screen. When I set it to tile the images, when it gets to one that is a larger size, it turns the outside parts of the image to stripes. Not only that but if you move a page around on the screen it makes more lines, almost like it's pushing them around.

The reason I'm concerned is a few months ago it crashed while streaming video, the whole screen went to vertical stripes and I heard a clicking noise. It wouldn't respond to any keyboard reboot, I had to hit the power button to turn it off and I heard a loud pop. When it booted again I ran disk utility and it didn't find anything serious. It hasn't happened since except for this desktop stripe thing that is happening. I remember my powermac years ago would tile the image around the large image, it would not stretch it to stripes. Anyone have any ideas if this is normal?