I have had my MBA for almost a week, and I've had no issues so far. Until now. This is the case: The fan operates as it should. It stayes on 2500 rpm at light use, and increases with heavier use. At 2500 rpm I was not able to hear it without putting my ear next to the keyboard. That was yesterday. Today the fan produces a new noise. It isn't very loud, but clearly audible at 2500 rpm in a quiet environment. It's a low, constant, buzzing kind of noise. It also increases with fan speed. What gives?