Ticking Sound from Under the Hood Help

Guys and gals, I know this is a broad question but I figure I'd give it a shot- Every now and then, when my truck idles, there is a ticking sound coming from under the hood. Performance wise, the engine feels fine. Sound wise, the ticking sounds like it is coming from outside the engine, in between the pulleys and radiator. I've looked in the engine bay while its making the noise but didn't notice anything. Does anyone know of something that could be loose or shaking to cause this? It started up again yesterday for a few but went away quickly when I started driving and came to a stop on a slight down hill. Thoughts????

 

Mine does the same and did some searching on here after reading your post and someone suggested the water pump. How many miles on yours?

 

I got 133,0000 miles on mine.