I had a very similar problem with my Sony 46HX903, Sony s570 and Denon 1909. This started about a week after putting the system together. Only on blu ray. At first thought it was a slow layer change as it happened mid film. But it started to happen two or three times and if I rewound film it didn't happen again in the same place or at all. I put it down to a handshaking problem and was in the market for a new amp anyway. I don't think it's happen since I up graded to a Pioneer LX53. Now all gear is HDMI 1.4 compliant. I gave old Denon to my mate and it seems ok with his gear, he's not reported any problems. If it wasn't a handshaking problem, then the only other thing is the HDMI socket on the back of the Sony s 570 blu ray seems a little slack. I've stabilised this with a bit of blue tac top and bottom.
I wonder if HDMI 1.3 receivers don't like the new generation of HDMI 1.4 blu ray players? Which blu ray player are you using and is it HDMI 1.4?