replace SD card, it may be faulty. Had it on my D80, formatting fixes the problem but comes back when you least expect it. I as well had that with failing HDD and only NEFs would look like that. It has something to do with checksum/integrity of data pack. If you look closely, you may find even JPEGs sort of "scrambled", sometimes offset between lines may be just a pixel, sometimes more. On my card, it would happen when it was 75% full (so must me failed memory around that allocation unit).
cheers