I'm sorry to hear that you're having this issue.
I might suggest seeing if changing the resolution might help, but that's admittedly a bit of a "band-aid" fix. Does it do the same if you use a component cable connection?
If not, you might consider having the unit serviced. You can reach the customer service department at 800-SAMSUNG.
Every time I play any dvd, there are horizontal hash marks on the movie I am watching. I thought this was maybe due to interference from a crappy HDMI cable but I have bought a new cable and there is no difference.