If the brake producing a "jit jit" ear piercing noise when you press the brake pedal, it might be due to the disc rotor is not compatible with the brake pad. Suggest to diagnose at workshop to prevent brake failure. You may also determine if this brake pad is incompatible with the disc rotor with the below ways:
1. "jit jit" noise can be heard during low speed turning while braking regardless of soft or hard braking then most likely the brake pad is incompatible with the disc rotor.
2. If you have replaced the brake pad or disc rotor recently and a "zii zii" sound can be heard, it might be due to the new brake pad or disc rotor is too hard.
3. If you have replaced with new brake pad and disc rotor recently but the braking performance is poor, if might be due to the brake pad is not fully in contact with the disc rotor. For example if the brake pad is new and the disc rotor is old, therefore the contact point between this 2 item is not contacted fully, the surface exerted with force cannot be maximized.
4. Brake pad reached its life span. There is a metal protruding point around 2-3mm on the brake pad. When the brake pad is worn out and needed a replacement, it will produce ear-piercing noise when pressing the brake.
5. Braking system intruded by sand/dust.
Suggest to diagnose at workshop, usually the keypoints of diagnose are:
1. Check if there are foreign substances entering the braking system, clear off the foreign substances.
2. Check and adjust the clearance between brake pad and disc rotor.
3. Check if the brake pad has reached its life span. Replace if it is.
4. Check if the wear level is uneven on the disc rotor, if the uneven level is nor severe, can proceed to skim the disc and continue using it. If the worn level is sever, replace the disc rotor.