Samsung mentions that certain TV”s can make a buzzing noise. The fix for this is to turn down some Contrast which by default is set to 100%. Turning down contrast can reduce the buzzing noises.
If turning down screen brightness or backlight does not alter loudness of the buzz then it is probably the power supply unit. Consider having your PSU replaced if nothing else solves the buzzing noise problem. People are reporting that replacing the PSU ended the noise and they are now happy. You should consider scheduling a repair. http://www.samsung.com/us/support/