Sounds like low pads. many have built in wear indicators that squeal to warn you.
Are the rear brakes working normally?
When they have rust on them or you need new ones. Go have them looked at
I believe your 4-Runner has an option of either rear drum or rear disc brakes. If the squeal is coming from the rear and you have rear drum brakes, have them cleaned and adjusted. If the squeal comes from the front, a shim may have slipped off of one of the brake pads and is scraping on the hat of the rotor.
You can try but the squeal will probably come back. Brake squeal is usually due to cracked, glazed, contaminated or inferior brake linings.
in VW's when you have the breaks adjusted out too far they tend to grab when reversing. There is an auto adjuster in the rear drum to keep your rear brakes adjusting. If the brakes are worn out they will "hang up" after reverse and cause squeeling.
Well if its more of a squeal, your brake pads are probably low, and need to be changed soon. That will occur more likely if you have rear disc brakes.
There are a couple of possibilities. One is lack of lubrication of brake system moving and/or contact points such as between back of pads and caliper housing and/or piston. Another could be that, the rotors/discs are warped/distorted and need to be machined or more preferably, replaced. If you replaced the front brakes (example) and you still have a squeal, it's possible it may be coming from the rear brakes.
the brakes were not fixed properly some part is installed wrong
Something is obviously wrong with the right rear brakes. Have a trusted mechanic inspect the brakes NOW before you hurt someone or worse.
that depends greatly on what is wrong with them.
Is it drum brakes? It's time for an inspection unless you just wanna replace the rear brakes yourself.
If the brakes are disk on the rear they can't be push or pressed in they have to be screwed in by turning the piston clock wise try this it should work. That is what I did on my 1994 Nissan Maxima becareful not to damage the rubber dust boot on the piston.