Hm... this is not the first time I'm reading about failing fans on graphics cards... - but I have never experienced it...
"I just found part of fan blade at bottom of case." - that is very strange, also not the first time when someone complaining about damaged fan blades...
If the fans are clicking from the beginning, maybe they're out of balance? That would destroy the bearings in time...
I would be curious to see the broken fans... those with missing parts...