Mario Kart ds game flickering screen in sleep mode?

I recently bought a mario kart ds game off ebay. When I put it in my ds system, it played fine, but when I closed the cover to put it in sleep mode, it began making strange clicking sounds. When I went to observe but lifting the lid slightly, I saw that the screens were flickering unnaturally. However, when I opened it completely, it was fine. I know it isn't a problem with my system, since I tried it both on my new ds lite and my old ds phat. Is the problem with the game cartridge, and does this indicate the game is fake? Or is it just from use? Anyways, I would like to know it it will affect my actual gameplay in any way, disregarding the sleep mode part.