What is that thing clicking?

[SaberSix]

2001 5.2 2wd.... While replacing coolant after thermostat change I noticed clicking coming from a component behind passenger side head light. It's attached to the side of the engine compartment kinda over the passenger side wheel well (but toward front of engine compartment). It appears to have vacuum lines going to it. It looks like some kind of relay or solenoid. It's about 2"x3". I've never heard it clicking before. What is that component and why was it clicking?

 

[dapepper9]

Purge valve solenoid. In short, it allows vacuum to pull fuel vapors from the tank to be burned

 

[SaberSix]

Thanks...… Yeah, that makes sense. I wonder why I've never heard it clicking before.