The lens could be getting a bit of dirt build up- you could try cleaning it with a q-tip and a verrrrrrrrrry small bit of rubbing alcohol or use a DVD lens cleaning kit, available at most department and electronics stores.
You may also want to check the game discs themselves for any dirt or fingerprints. This can make it harder for the system to read the data- you can clean the discs with a soft cloth, wiping from the center outwards. Do NOT follow the grooves.