Prius makes groaning whistling sound

Has anyone had this happen to them? My 2005 Prius makes a groaning whistling sound(don't know any other way to describe it) when I turn it off. It started a couple months ago with a short sound once in a while but has grown into about a 5-10 second long sound when it is turned off. It makes the sound maybe 75% of the time. Shorter sometimes but up to 5-10 seconds other times.

Checked all my fluids and looked for signs of a leak but have not found anything out of the ordinary. Car runs fine, starts no problem, isn't running hot, gas mileage has dropped off but it has gotten colder and I have put on new tires a month ago.

I have noticed once when I first started it, it made the same sound but for only a second.

Is there some thing in the hybrid batteries or charger that may do this when it starts up? What about the CVT maybe there? The sound comes from the front of the car.

It had a complete major check up less than 7,000 miles ago.

Any help or ideas would be greatly appreciated.
My 2005