If you ask me, there's not enough detail in the description to make any kind of guess. Where was the steam coming from? Did the clicking noise vary in speed with the rpm's? What part of the rpm band were you at? Have you looked at your fan blades? A grenading water pump impeller doesn't make much noise; once it goes, it goes- even if you could hear it, the noise wouldn't linger on like that. If I had to make a wild guess, I'd say something's not right in the cylinder head . . valves?