I have a 12" powerbook that I bought about a month ago. I usually run it in "Normal" power mode even when it is plugged in, just because it stays so much cooler. The fan comes on occaisionally and if I'm doing something really CPU and/or disk intensive the fan can spin quite fast and make a good fair amount of noise. I understand this. Just last night though, the loud "whirring" noise is accompanied by a loud buzzing noise. I've seen this before in a desktop PC when either there is a lot of vibration in the case caused by the fan, or if a loose wire is resting just with reach of the fan blade tips. This really concerns me in my powerbook. I can't imagine what would be vibrating, its certainly not anything the book is resting on (I can hold it in my hands, put it on a table or balance it on my lap and get the same thing). The buzzing is so loud that its quite remarkable even on the other side of the room if there isn't any noise in the house. My wife remarked on it immediately when it first happened and she was sitting in the kitchen about 12 feet away from me. Any ideas?