Your car gives a whistle like noise when you press on the brakes?

Look at your brake pads. You probably need new ones.

is also possible that the pads are okay but maybe the last person to replace the brakes didn't use the disk brake compound on the back of the brakes. Disk brakes are notoriously noisy and can squeal, even when the pads are in good condition. Disk brake dust can make the noise even worse.

If the brake pads look good, use an air compressor to blow the dust away from the brakes. Make certain that you don't inhale any of that dust though, maybe you could find a dust mask or respirator. If the brakes are worn, have a qualified mechanic take care of it for you or if you decide to do it yourself, make certain that you understand what you're doing.