some of the Barracuda 7200.11's needed a firmware update, use the link below and enter your serial number in to see if it's one of them that needs it. When you update the firmware you won't lose the data on it.
http://seagate.custkb.com/seagate/crm/selfservice/search.jsp?DocId=207931
I would try that 1st then run a full check in windows on the drive and see if the clicking stops, if not get a 2nd drive and backup onto that first then do a low level format on the bad drive. If all that fails send it for RMA means it's failed.. Seagate make great drives but there always will be the odd one that dies from bad components.
If while trying to update the firmware it can't detect the drive, remove all drives that are connected to the motherboard and then try again.. again if that fails move the drive to a different SATA port on the motherboard and keep trying it will finally see it, I have heard of this fault before and had to fix such a drive this way

.. you may find you need to move the drive to another PC with a different motherboard too to do the firmware flash.. Depends on your motherboard.. Also a good time to update your motherboards BIOS if you have not done that in a while, it may help with detecting the drive.
This only applies to external drives.
If the drive is an external drive and you are using E-Sata and the drive still won't detect for firmware flashing, try plugging the drive on the sata connectors on the inside of the motherboard.
If you are using the USB and have no E-Sata and the drive still won't detect for firmware flashing, you may need to remove the drive from it's case and plug in a sata cable to it and again connect it to the sata on the motherboard.