Newbie blu-ray problem

[trekgod3]

Hi everyone, new member and blu-ray owner here. We just got a Memorex MVBD2511 from Wal-Mart for $148 a few weeks ago. It is connected via a HDMI to a 51" Hitatchi 1080i projection HDTV. I bought four of Wal-Mart's $10 blu-rays- Terminator 2, Saw 1 and 2, and Stargate. They all play fine-menus load quickly and are responsive-no picture or audio problems. The problem I have is with Hancock and The Dark Knight. Those movies will play for about 10 to 30 minutes then suddenly the screen goes snowy (like tuning in to a channel you don't get on a really old TV) and the sound goes out,too. The disruption lasts for 5 to 30 seconds, then the picture and sound come back on. If I unplug and re-plug the HDMI, it comes back on,too. At first we were using a $15 Walmart HDMI, but I just switched to a $50 Rocketfish cable that is rated for 10.2GB/s and 120Hz. Still having the same problem. The other thing I noticed was the underside of the discs. On the four cheapies I got at walmart, they look like a shiny regular DVD or CD looks. But, on Hancock and the Dark Knight, the underside is shiny and has a wavy rainbow pattern-kind of like an oil/gas spill. Any ideas? My next step is to get a set of Component cables and see if that makes a difference over the HDMI.
If someone could check the undersides of their copies of Hancock and Dark Knight, I would appreciate it . My mother-in-law bought them for us for Christmas from an online store. Thanks for your help!