What's This Noise? Clicking After Shutting Off

[heavy4x4]

Can anyone help me identify this noise? I've been trying to troubleshoot some recent fuel delivery problems that I've been having, and I heard a noise that I had never noticed before. Not sure if it's normal. With the hood open and the radio off, I turn the key to the 'on' position and hear the pump prime for about 2 seconds. Then, I turn the key to the 'off' position and I hear a series of rapid clicks coming from the engine. Had a buddy run the key while I listened for it and it definitely sounded like it was coming from the throttle body area.

 

What is this noise? Do all trucks do it? Mine is very repeatable.

 

2000 Silverado with the 5.3L

[Zembonez]

What is this noise? Do all trucks do it? Mine is very repeatable.

My 07 makes a series of clicks (sounds like relays) after the key is turned off. Only lasts a second or so. Not sure if that helps any.