Well heres a good reason why it happens... First answer this question... does anyone smoke in the house? if the answer is yes, ok, If not can you smell food cooking, or incesne burning from the room that you game console is in?
If you answered yes to any of these questions, And do not care about voiding your warranty, I can tell you what I did to fix mine.
First you need some supplies, a good precision tool kit or computer tool kit, Windex, Canned air (DO NOT USE AN AIR COMPRESSOR), cotton swabs, very importantly some refrigerator magnets and a sheet of white paper.
The magents go under the white paper so you can put the screws down and not loose them on top of a whtie piece of paper.
First you open the case, then look for the dvd drive, take out the little screw around the perimeter, and pop off the top of the dvd drive... you may have to move other things to get to it but I can't sit here all day and re-do this for you, once you have the cover off, you should see the lens, don't blow on it just put a little glass cleaner on the cotton swab, and lighty make circles on the lens, you shouldn't have to scrub, now use the dry end to get around the edges of the lens to ensure there is no liquid left.
Now since you have it wide open, go ahead and dust out the inside with the canned air, this is why magnets are important, so you don't blow the screws all over the place.
Put it back together, and commence playing.
Since I did this last year I have no problems.
