Instructions
Turn off the Xbox 360 and disconnect all cables, as well as the hard drive and any other attached peripherals. The clicking could be caused by the system overheating, causing difficulties when accessing the hard drive.
Allow the unit to cool for at least 30 minutes. While waiting, ensure that the Xbox 360 is placed in a well-ventilated area and that the fans are not blocked.
Reinsert all cables and the hard drive and power the system back on. If the problem persists, your Xbox 360 hard drive is either going to fail or already has.
Back up any data from the hard drive to an Xbox 360 memory card or properly formatted USB stick, if possible. Any items you have purchased, as well as your Gamertag, can be re-downloaded provided you are still connected to Xbox Live, but you cannot recover data such as saved games from the Xbox Live service.
Reformat the Xbox 360 hard drive by navigating to "My Xbox->System Settings->Memory," then highlighting the hard drive. Select the "Format" option and choose "Yes" when prompted to confirm the selection.
Enter your console's serial number, if prompted; this can be found on the back of the Xbox 360 console above the Ethernet port. Select "Done." This step is included by Microsoft to ensure that no accidental formatting occurs.