Just to make sure that it's the Northbridge fan itself, I would stick a toothpick in the fan to stop it and see if the noise stops. If the noise does stop then you know that it is that little fan.

If the fan is removable, Radio Shack stocks little fans for this exact situation. They clamp on like an old AMD K6 fan, but they are real small.
scottjamez Reviewed by scottjamez on . Quick question (for the comp people) Hey i hear a loud buzzing noise coming from my pc. I opened it looked in it i orginally thought it was my heatsink fan buts its not. Its a little fan ON the motherboard. And i would like to know what is causeing it and how i can fix it and what the fan is named. I would really appreciate it cuz the fan is not spinning properlly because of this and i dont wanna fri anything. Thanks allot guys Rating: 5