All the failure thresholds read "OK" so as far as the onboard diagnostics go, everything is fine. But all that means is, whatever is causing the clicking noise isn't something the SMART system can detect. Such clicking is abnormal, and as Scout101
said, your first priority should be to back everything up that's of value to you from this drive, before it simply fails.
I was hoping the SMART utility could point to a specific problem, but whatever is going on isn't something it can detect.