Just in case.
Generally a clicking sound coming from your hard drive is a bad omen. Secure your hard drive in place, back-up anything important to another source. Scan the hard drive with chkdsk command. CHKDSK C: /F /R
/F Fixes errors on the disk.
/R Locates bad sectors and recovers readable information (implies /F).
If CHKDSK offers to "convert lost chains to files", recover lost data, or fix something else, you should accept.
After CHKDSK finishes, restart your computer normally and see if the dreaded click of doom returns. If so, the drive is most likely damaged, and/or should be replaced as soon as possible. Especially if there are a lot of bad sectors.
Using Windows 7