How old is the PS3? It's possible it's just a little dust or a smug on the lens so like Oniya I'd say try a little compressed air or if it was the top loader maybe try cleaning the lens gently. If your the adventurous type and good with electronics you could also try replacing the disk drive yourself. Actually started looking at instructions for how to do so after reading your post and it shouldn't be very hard, just looks scary to do.