Ooh, you should never do that, you need to let your macbook warm up to room temp. before turning it on.
you risk condensation forming inside a rapid warming macbook as the fan shuttles WARM air in the room over the COLD logic board
its not the fan you should worry about, its doing that and causing condensation and corrosion to form from quick temp. fluctuations inside the cold macbook.
DONT do that again, it leads to corrosion.
A: you notice it more in a quiet room (the typical case) which is normal, all is AOK
B: fuzz and dust has caked onto the blades causing the fan hub to get off balance and make a buzzing sound.
C: fan rotor is going bad and making a whirring or buzz noise (rare).
D: Fan is spinning up due to excess heat from gaming, heavy graphics (typical, all is OK)
A and D are normal
B and C are not.