I recently purchased Dynasty Warriors 7 to play on my PS3 Slim 160 GB (2501A) and whenever a bunch of enemies appear the game slows down quite a bit and the graphics look worse/less smooth. I don't have a problem with lesser graphics, but its kind of annoying going in between good graphics/smooth action and then a big slowdown in speed and lesser graphics.

Any suggestions or ideas at what the issue could be? I bought the game brand new and I found no scratches on the disc. I don't have this slowdown with any other games.