stop each of the system's fans one at a time by gently pressing on it's center.
if the noise stops along with one of them then you have found the culprit.
and what makes you so certain that it wouldn't be the power supply?
the noise was already present before installing this PSU?
and what type of "buzz" is this noise?
what could be the problem and is it bad?
there are many components that can vibrate in place, rub against each other, grind bearings, etc that can produce many types of noise some may consider a buzz.
without you pin pointing the exact source of this noise there is no way to determine if it may be "bad" or not.
include your complete system specifications.