Did the buzzing noise change anything to the configuration of your computer?
If this is a continuous sound, it might be due to the fans that are overworking to cool down the heat of your pc. However, if the sound is too loud and that you want to decrease it, there is a software that you can choose to download - Rivatunner that will hence lower the fan speed. if the problem persists, i would sugest you to try to see a professional