Ping/click When Ignition Cycled On. What Are The Sequence Of Events When The Key Is Turned On?

When I cycle the key on now, I hear a strange metallic sounding 'ping' or click, coming from around the intake manifold (the fuel pump has shut off by this point. Maybe 1 full second afterwards).

What are the sequence of events when the ignition is cycled on (but not cranked). Do injectors pulse? Does the IAC valve do something? I really can't think of anything else in the vicinity!

Thanks guys

Tis the IAC, it seems. It seems to respond well to 12v, but should it make an audible click when ignition is turned on, after the fuel pump stops?