buzzing noise coming from MBP

Yesterday my four week old MBP started making a buzzing sound when I first powered up then silently goes away after two or three minutes. It sounded like a bad bearing in a fan but I could figure out the location of the fan. I was worried about a malfunctioning fan in my new laptop so I brought it to the Genius Bar. After troubleshooting for awhile in a back room the Genius returned and told me that an inverter for the backlighting of the LCD was acting up. Since the laptop was practically new the Genius swapped my laptop with a brand new unit. I asked the Genius if this was a common problem and he said that this was the first he'd seen with the MBP Core2Duo. I just wanted to pass on my experience so that people will not mistake the sound for a fan problem and maybe have another look by Apple before your Applecare or warrenty runs out. I have really enjoyed my experience with Apple's service and products and there is no turning back. Way to go Apple!