Overheating, but only for certain games

So, I bought the Saints Row Double Pack a couple of days ago. I go to play Saints Row 2, and after only a couple of minutes of being on, I get the two red lights and it shuts down, and the disc itself is also hot. The same thing happens with Saints Row 1. But my other games, Fallout 3 Game of the Year Edition, Fallout New Vegas and Elder Scrolls IV Oblivion don't do this, and after an hour or two of play, their discs aren't nearly as hot as the Saints Row ones are. My console is out in the open, on top of a hard, solid surface with nothing on top of it or on top of the vents, and it is not near any other heat source. The power brick is in the same situation. In late 2006, I was able to play Saints Row 1 without any problems at all for hours on end, so I don't know why it's doing this now. I have a 20 gig Pro from 2006, if it matters. Never got RRoD, never had to be sent in for repairs or anything. This is the first time I've ever had actual trouble.