I don't actually know, but I recently noticed the same sort of stripes on a picture my dad had taken. He told me that it was an abberation of some sort in the sensor because it was straining to take in photons in a low light situation. So when you take pictures in very low settings I think these lines show up where the sensor is not as strong as the rest of the sensor (or whatever it is that takes in the light to create a photo, sorry I don't know much about digital jargon). You might check back later to see if he also posts a more coherent reply.
rg2 *PENTAX SAMURAI*
