PLEASE BACKUP IMMEDIATELY!!! The first moment you notice your drive is clicking occasionally that means there is a problem brewing.
There is nothing worse to a computer user than losing data. Do not let it happen to you.
If you dont have other drives, get a DVD burner and a stack of DVD+Rs. This will cost you less than $100.
Back everything up. If you care, do it twice!! Discs do fail.
Then, once everything is backed up, run the manufacturer diagnostic on the drive. Backup first, sometimes the diagnostics can damage data. Run the full test. Let it run as long as it needs.
If it comes back clean, run it a total of 3 times. If it's still ok, then you can breathe. If your drive fails the test (which I think it will), then you can RMA it to the manufacturer (assuming your computer isn't an OEM like Dell etc... the drives in OEM systems are warrantied through the OEM, not the manufacturer). The only cost to you is return shipping and some time on the web / phone to setup the RMA. I am amazed how many people just go out and buy a new drive.
Good luck. Let us know how it goes
~MiSfit