well this is an odd one.
So it does it once when you turn off the AC or the engine... then it stops? No more sound? More of a squeak? Did you open you hood and find an Owl yet?
Check your serpentine belt or acc. belt to AC. They will slip or squeak out some strange sounds sometime.
You can also apply belt dressing to help with squeaks ......as long as the belts are not too tight or loose.
2017 Axis / 25.4: Big Foot Levelers, Aims 1200 Watt inverter, Ceramic Window Tint, Full River AGM 6V batteries, Front Hellwig Sway bar / Rear Track Arm, Safe T Plus Steering Stabilizer, PD 4655 converter, Hard Wired Surge Guard, WEboost + WiFi Ranger, LED Headlights/Driving lights, Fresh water surge tank, Black Tank Tornado flush, 4999 zip ties.