Why does my MacBook Pro click?
There is a constant clicking when MacBook Pro is on.
Apple的 MacBook Pro 的產品線是專為可望極致效能專業使用者所打造。MacBook Pro 产品线包括了MacBook Pro 13" （一體成型機身款）, MacBook Pro 15", MacBook Pro 15"（一體成型機款）, MacBook Pro 17" 和 MacBook Pro 17" （一體成型機款）。
Three possibilities for a clicking noise. 1. Optical drive (unlikely) 2. Fans (tossup) 3. Hard drive (very likely) If the computer were mine I make sure I had a good backup and replace the drive. Since you didn't say which model you have I am including the repair guide for the Core 2 Duo. I will also include guides for identifying your computer and for possible replacement hard drives. Ralph
I have a Macbook Pro that had the exact same problem, well that was not a problem actually.
Does it happen when you lift or move your macbook pro while turned on ? It probably comes from the HDD, it is called the Sudden Motion Sensor (SMS)
When the system detects sudden acceleration (such as when the computer is dropped). It disengages the disk heads from the hard disk platters, preventing data loss and drive damage from a disk head crash. As it must be really fast when it hit the floor for example, it produces the "click" sound.
If you want to make sure that it's the reason why it clicks, hold your mac while powered and shake it a little, if it clicks, that'll be ok.