Most likely the brakes. Try to get someone to stand outside the car when backing up to try to localize it. Had this happen on a Toyota. Next brake job got hardware and pads replaced. No more squeal.
You Dont Grease It Up enough
If it only happens when backing up, you may have the parking brake engaged.
Free Backing brakes have a unique design that moves the front brake shoe away from the brake drum when you are backing up. This allows the trailer to roll free when backing up, but this type of brake has no braking power while backing, therefore, your tow vehicle's brakes carry the entire load.
Backing up while driving is putting your car in reverse with your foot on the brake and slowly letting your foot off the brake. If you are pulling out of a parking spot you might turn the wheel.
The squeal is a warning device installed on your vehicle telling you that your brake pads are worn out. The light is coming on because you have a problem. Have your braking system inspected ASAP. Do not ignore this or you will end up replacing the rotors and spending more money. You may also end up having an accident due to defective brakes.
Bike brakes squeal due to vibrations between the brake pads and the wheel rim. To fix this issue, try cleaning the brake pads and wheel rim, adjusting the brake pads to align properly with the rim, and using sandpaper to roughen up the brake pads for better grip. If the problem persists, consider replacing the brake pads or seeking professional help.
the clicking sound is usually made by a device fitted to indicate worn brake pads and only happens when braking whilst backing up, many vehicles have this feature, check your brake pads for excessive wear.
failing brake caliper caliper seizing
check your parking brake or check the ring and pinion in the rear end
Possible parking brake problem. Check the p-brake shoes inside of the rear rotor.
It can be several things, either by themselves, or in combination. 1) the belt has dried up and isn't as grippy any more. This causes it to slip and squeal. There are sprays available to restore grip on belts which might help. 2) the belt has stretched a little, which causes it to slip and squeal. Retension, usually by adjusting the alternator position and it should be OK. 3) one of the auxilliaries(alternator, power steering pump, water pump) is about to seize. If it's harder to rotate the belt will slip and squeal.