I've noticed that there is a chittering type of sound that is coming from a particular location under the hood when I turn off the car. It's not the radiator/fan. I took some pictures and will upload them from my phone now...

 

It doesn't happen for long. I just had the radiator fan/motor replaced and got a new battery but it still happens occasionally (I don't always notice it). It's not that loud but noticeable and it doesn't drain the battery. Might it be a belt of some sort?

 

Can anyone ID or guess the component under the box?

 

The components inside the box are computers, the engine control unit and transmission control unit. They don't contain any moving parts. (Or maybe they can contain relays?)

 

That makes sense. Thank you for satisfying my curiosity. My car hasn't made that noise recently. I think it comes from somewhere below that area because when I removed the top to that area, the noise grew louder.

 

There is a fan mounted in the bottom of that box to blow cool air onto the control units - I don't know when it runs -

 

It's been over 100 in San Antonio and that's when I've noticed it. Maybe the fan is aging or maybe it's just noisy.

 

Yes, replace that fan. If it quits, you'll overheat the two modules and you will have a mess.