Diagnostic help- strange whirring noise?

Welcome to the forum, fellow Michigander!

The usual noise after power-off is the hot coolant getting pumped into coolant heat storage, which serves to help reduce fuel consumption when starting up the next time around.

The whirring noise sounds like it might be the brake booster pump and/or accumulator. An old thread cited this as a way to confirm:

As for the coolant otherwise, are you getting any codes related to the inverter cooling system? Usually, you'd get something like P0A93 if there was a leak or the pump sensor thought something was off.

 

welcome!
how many miles and how long have you owned it?
definitely a leak somewhere

 

The inverter coolant path is not very complicated tracking a leak should be quick . Invert fluid not flowing and that system getting hot could produce strange noises. And for sloshing . After car cools move plastic re. I've radiator cap. When you remove the cap you should see coolant or water standing proud at the top of the neck almost ready to dump on the ground what do you see when you remove your radiator cap at a cool state of the vehicle . If you can look down that black plastic filler neck and see nada that maybe part of sloshing . Systems needs be FULL.

 

So look at the picture on Google of inverter coolant loop for the model car you're talking about..

 

was the inverter or engine coolant exchanged, or both?