I own a 2008 Ford Escape Hybrid and when I step on the brakes (how hard I apply the breaks it does not matter - it always happens at low speeds) it makes a loud noise as if the disk brake is not well secured on its mount and the breaking action is forcefully shaking it off its mount.
Take the vehicle to your mechanic and ask him or her to inspect the brakes. Describe the problem to the mechanic as you described it in your post.
Sound like you should see either the dealer or someone with a clear understanding and training of a Hybrid brake system.
When you step on the brake pedal the brakeson the car don’t necessarily apply. The noise may have nothing at all to do with the conventional brake system.