Clicking hard drives (louder and clunkier than usual) often suggest that the drive is about to die.

The only way to identify it, is to isolate it. You'll have to open up the case and pull the power wires and fire up each other and us the computer to look for the sound.

do this:
- disconnect all drives except C: (your boot drive) look for clicking
- if no clicking heard after some usage, power down and add one drive. Repeat

There's no easy way.