I'm not an expert, but another possibility is that you're picking up RF interference from somewhere. I had a PS2 with similar issues in which I would see horizontal lines whenever I played DVDs on it (games seemed to work fine however).
At the time I was using the stock RCA composite cables that came with the console. Once I upgraded to component cables, the problem went away. The important thing to note is that neither the cables nor the PS2 were bad, but rather there was systemic noise that was affecting the analog connection between the PS2 and the screen.
Unfortunately, there's no guarantee that just switching to component cables will get rid of the problem, since any analog cable will be sensitive to RF interference. The only way to fully rule out RF noise is to use a digital standard (DVI/HDMI).
If you want to be geeky about it though, you could try things like surrounding your player and cable in a Faraday cage, or at least cover the cable in some sort of grounded shielding to see if the problem improves.
