Clicks can vary; sometimes it's just safe thermal compensation or even failed-sector remapping (a good thing, at today's densities)... other times, it's varying degrees of horror. I had a problem with a clicky WD semirecently (80gb WD800AB), and the best theory I could come up with was that power supply voltage was sagging enough to kick in an overly-aggressive protective-parking feature... Had to RMA the first one, and the second behaved the same but without data loss; never did test it by installing a higher-wattage supply, and theoretically I was within spec (just like the 6000RPM-to-goose-the-benchmarks drive was theoretically a low-power 5400RPM)...
Er, back to how much Conner did/didn't suck, I was running a 'naturally selected' one (800-something MB, made right before they were bought up by... who bought them up, Quantum?) that had been in use for about 8 years, with no trouble. As ever, when a drive does start to go, nothing to do but replace it and hope you have better luck the next go-'round.
