Brake Abs Warning Light problems of the 1999 Toyota Avalon

It has happened on level surfaces as well as inclines. When you step on the brake, they first make a grinding sound. Then, immediately after, they make a sound like a metal spring uncoiling (like a clicking, otherwise). After that, you are free sailing as you have no brakes! this has occurred several times while either trying to brake or even after braking successfully and then all of a sudden they let loose while at a stop causing the vehicle to accelerate forward. I have thankfully been able to avoid any serious injury or accidents, however have had a minor issue with hitting a fence due to the brake failure. We have had the brake system checked for any repairs needed only to be told that there is nothing wrong with the brake system. Also note that the abs light and traction lite often comes on dash even on dry surfaces. This braking problem is something that happens in the sienna, but in other model Toyotas as well. Currently, it is only the prius braking system that is getting public attention, however.