You have to be more specific than that. What is making the clicking? The lid, the inside of the computer? Does it keep clicking or is a long click? Does it only happen when you wake it from sleep or also when you turn it on?
If it makes a long click only when you open the lid from sleep or turning it on and it's coming from the machine itself, it's likely the Harddrive turning itself on again. That's normal.
If it keeps clicking, it might be a faulty Hard drive.
If it's the lid that makes the noise also when the computer is turned off, it's the hinges that are too tight.