So late last night, I was watching a DVD on my MBP while it was on my lap. I accidentally bumped it with my leg while getting up and it started making this annoying buzzing sound coming from the left upper corner. At first I though it was the superdrive spinning up, but I ejected the DVD and it continued to make a buzzing sound. After some Googling, I found that it was probably my fan making this sound. After a little bit of shaking, the noise stopped. I left my MBP on overnight and when I woke up, I noticed that the buzzing returned. Again, I shook my MBP lightly and the buzzing stopped. I then booted into Windows and played some FPS games. After rebooting into OS X, I noticed the buzzing returned. I concluded that my left fan must be loose, and that at a relatively high RPM, the fan must shake enough that a slight jostle will cause the fan to hit something, causing the buzzing sound. I tested my theory by using smcFanControl to amp up my fans to 4000 RPM and give my MBP a slight jostle and sure enough, the buzzing started. I made an appointment at my local Apple Store's Genius Bar, so I'll see what the Genius says. Question is, if it does turn out to be a loose fan or whatever, how long can I expect repairs to take, and is this the kind of repair that can be done in store, or do they have to ship it to a service center?