My computer(CPU) makes similar grating noises on start-up and continues till I actually slap my hand across the the top a couple of times. As far I can tell the sounds reduces in volume to a bare minimum and then gradually stops. but if I restart (switch off and restart maybe half an hour or an hour later) the machine again in the course of the day it won't make any noise. But if I restart(just restart) the machine when its still noisy it has no redeeming effect. I moved The wires away from the fan but to no avail.
I had the same noise as well a while ago and it was one of the fans that had gone bad (probably the bearing). The only solution I know of is to disconnect each fan one at a time and pinpoint the source of the noise. Once you find out replace the fan.