Western Digital Master Race :carling:
Oh, and I've never heard any "clicking" come from my WD Drive :p
It depends on load from what I remember. It's usually the actuator arm that produces the sound, after drives age and wear down or under extreme workload they'll slam into the stopper and it produces a click.
Can't be bothered to explain it all but there are a multitude of things that cause it, I know with my old WD drive is that the head went bad and it couldn't detect where it was on the platter and it would slam back and forth until it died. I have never been so pissed in my life until that happened.