If you've been keeping up with MacBook sans-Pro news, you may have heard something about an infamous "moo"-like noise coming from the fan. Basically, the fan goes on and off and on and off and on and off continuously, in a vain attempt to keep the machine cool. Now, I'm no engineer, but it certainly doesn't take one to recognize that this isn't normal behavior. (MacRumors discussion here, video of the fan problem here.)
I took my black MacBook to the Genius at the Apple store (Oakbrook, by the way) to get this fixed, and his response? "It's normal. A fan will do what it needs to do to keep the machine cool." Gee, thanks.
As you may remember, I had a similar issue with my MacBook Pro. A new fan unit later, this problem was fixed, which certainly leads me to believe that this isn't normal behavior. (I also showed the problem to a friend of mine who is an engineer, and he confirmed that this isn't normal.) I've called AppleCare (an almost guaranteed better experience, every time) and a repair box is on its way. Sigh.