Well, clicking is generally a very bad thing. The first thing to do is to copy off the drive everything that you can currently access.
What I would do then is to remove the drive from the external enclosure and attach it directly to my desktop system's motherboard. Do you have a desktop system available? This is to eliminate the possibility of the problem being in the external case electronics.
Then use a recovery program, such as Recuva, to copy off the drive everything that can be found. Then you can either RMA the drive (if it is in warranty and there is no sensitive data on it) or trash it. If you want to, download the manufacturer's diagnostics and run them to see what they think of the drive, but I would never trust my data to a drive that has been clicking.
Best of luck.