Ah, back to CoD -- brings back unfond memories.

The best writeup I've seen (from someone without a vested interest) is by Steve Gibson (author of Spinrite): http://www.grc.com/tip/codfaq1.htm and the subsequent pages (links at bottom of that first page). Quick summary: Clicking is a symptom, not a cause; and CoD is rarely contagious, widespread worries to the contrary notwithstanding. Mr. Gibson describes the rare case in which destructive contagious behavior is possilbe.