Hi, I was wondering if anyone knows what this strange sound is before car is shut off. I don't think it's coming from the engine. I had someone shut the car off while I was trying to hear for it at the engine bay. Sounds like it's coming from underneath somewhere.

 

At a best guess, I'd say check the serpentine belt to see if it shows any signs of damage or wear.
See if the non-ribbed side (the flat side) looks to be glazed.
The noise is super brief, so my best guess is it's the belt.

I know you said it sounds like it's under the car, but belt noise could travel in all kinds of directions.