Recently (April 2009) after getting a new macbook, i realised that under the “W” key, there is a static hissing noise. I had several conversations with apple support and then had the book checked at apple store at regent street. Apparently the sound is a very slight noise, and without a good hearing and a slient environment, its very hard to detect it. I had it replaced and still the same thing happened, and I have noticed that previous versions also had this problem. In many discussion and forums, this problem is caused by a “sleeping” second processor. You can “fix” this by installing QuietMBP and dragging the bar. So its not a problem as far as I can see. Its just irritating for those with sensative hearing.