My xbox 360 will go open tray for hours and after reopening it will finaly read the game. It takes around 30 - 60 secends of reading for it to give up. However sometimes(rarely) it goes unreconized disc. The xbox 360 is 4 years old and original. The laser seems to make some swissing/swishing sound. Is it a dirty laser lens because I have never cleaned it in all these years. What are signs of a dirty laser and not some other problem.