pop/click noise from serpentine belt 02 GT Auto

[Temecula_GT]

most noteable at idle. there is a distinct click sometimes followed by a lower pop noise coming from one component on the serpentine belt if directed to a good diagram I can then identify the component and describe the behavior in detail. Please help - need diagram for starters

 

[02GTstangGT02]

not the best diagrams...

 

[02GTstangGT02]

here's a better one

 

[Temecula_GT]

It was the AC. Don't I feel silly. I'll try to ask a more intelligent (informed) question next time. Thanks for the views - very helpful.