Strange under hood sound with ignition off.
 

So I gave the car a quick wash tonite, and opted the hood to dry inside, and was greeted by this weird slow pulsing nails-on-a-blackboard sound. This is with the ignition completely off for about 30 minutes.

https://youtu.be/cb6H8vjkWPc

I hope the link works, not real confident on posting video links.

that is very weird. according to the video it is loud and high pitched.
maybe the horn got bad? unplug the fuse see if it does it again?

A/C pressure bleed down. This one is louder than the other post a few days ago.

https://www.camaro6.com/forums/showthread.php?t=448477

Sounds like the same thing. It seems to be “normal”, but it definitely shouldn’t be. I am an engineer at a company that makes ice cream machines, so I’m familiar with refrigeration systems, and if our machines made noise like that we wouldn’t sell any! 😄

What company do you work for?