When I turn the car battery on, there is a loud squeal noise

When I turn the key to that position that turn the battery on, the car gas a squeal noise that never goes away. I have turned everything off (ac, lights) and it wont stop. What movie parts are going on in the car when the battery is just on? Any way to fix it? Thanks

There's a couple of things which activate with the electrics, so it depends where the noise is coming from.

If the noise is coming from behind you (under the rear seats), it's the electric fuel pump.

If the noise is coming from the engine, it's the servos on the injector system winding up into position. I get a buzzing noise for a couple of seconds, then it switches on. I think it's the idle control motor.