It could be that your screwed the fan too close to the frame which is now causing vibration, also, check your HD, I had a problem where I thought the noise was from the fan, though after lengthy investigation,
-slimpiggy(瘦猪犹如插翅虎);
2001-8-30{73}(#184820@0)
I had founded that the noises are actually from the old 5400 HD (spining)
I had the same problem. After removing the fan, I found the power supply became very hot. I find nowhere to sell the fan separately. I had to buy a new power supply, wich cost me $20.
-larryxliu(bubble);
2001-8-30(#185131@0)