easy now, you all are makin him tear everything apart
here's the way i test: i take a q-tip, for example, and i stick it a bit off center, still on the flat surface of the fan, not on the blades, and gently push on it, to slow it down (not to stop it)
if the sounds goes down, you can figure out which one it is. make sure you touch the metal part of your case before you touch any of the components (to avoid electrical arc).
best of luck, let us know wat happens