What is the MacBook Moo!?
Many users have observed that their Apple MacBook makes a mooing sound. The mooing sound is caused by the fan
starting up and then immediately stopping over and over again. You can listen to a recording of the moo here, or
view a video of a disassembled MacBook mooing here. The noise becomes
very annoying when using the MacBook in a quiet environment
and as yet Apple have not admitted this is a fault or produced
an update to change the behaviour of the fan controller.
MacBook SMC Firmware Update - 17th August 2006
An official fix has been released by Apple! "The SMC Firmware Update adjusts fan behavior in the MacBook."
I have just installed this update and found that the fan is on (its lowest setting) even though the system temperature is only 51 degrees Celsius. So the fan behaviour has definitely been changed and will hopefully mean no more mooing! Whether it is merely a coincidence that the fix has been released in the same week I brought this to the attention of senior executives at Apple I do not know. Many thanks to all of you that signed the petition, I am sure together we made an impact on this.
I noticed that the mooing noise only happens when the processor is between 65 and 67 degrees Celsius, the annoying thing being that this seems to be the temperature at which the processor idles at. If the temperature rises slightly above this then the fan will come on constantly at its lowest speed. This is far less noticeable than when the fan is repeatedly turning itself on and off (a.k.a. mooing)!
I created a Dashboard Widget that monitors the CPU temperature and when it enters the "mooing zone" (65C - 67C) it increases the CPU temperature by a couple of degrees so that the fan stops mooing and stays on constantly. See the FAQ for details of how it does this. The widget can be turned on or off easily using the icon placed on your dashboard.
This is a rather crude fix to the problem and I hope it is only temporary. If you also experience the mooing problem and would like to see it fixed by Apple (hopefully in a simple firmware update) then please fill in the petition below.
Update 17-08-06: Apple has released an offical fix, (please see above).