Loud buzzing is caused by many things, all power related. However, you need to be more specifc about the sound to be sure of the diagnosis. Is it a loud buzz, a low buzz, high frequency, low frequency, when does it shut off? Does it change pitch, etc.
Modular PSUs are famous for the trouble you describe.
Yep, check power connectors to see if they're tight. Arcing may produce heat and shock your system with fluctuations.