hmm, you could try oiling or greasing the motor or something if its possible. When I was young I used to have an remote controlled car and I forgot to add oil to the engine when I built it, It was skreechingly loud until i fixed the problem. You could try putting something to absorb the sound and vibration around it so it wont make so much noise maybe?
So is it the sound your actually getting coming from the bearings? Or is it just the sound of the fan istelf. A friend of mine has a squirl cage that sounds like a 757 when it kicks on!!!
Try using a small amount of wd40 spray mate, that often does the job.
also perhaps try a tiny drop of bike chain lube, a very little amount, about a matchsticks head worth