It's kind of a pain in the behind on V brakes. You loosen the allen bolts or whatever that hold the shoes to the brake arms, and make the front of the shoe touch the rim before the rear. What happens is the whole shoe touches the rim at once, and begins quickly vibrating front to back. The brake grips the rim, flexes, and then lets go over and over . The vibration is heard as a squeal. A little hard to explain, hehe. With the shoes toed in, the vibration is stopped and the brakes are once again silent.,,,,BD
At least yours are adjustable, I just had to bend my old vintage brake arms to achieve the same effect.
So many bikes, so little dime.