If the disc rotor producing a "jit jit" ear piercing noise when you press the brake pedal, it might be due to the disc rotor has reached its life span or has uneven wear. Suggest to check the disc rotor at the workshop. You may also determine if the disc rotor has been fully utilised with the below ways:
1. If you have brake pad replacement frequency, then the wear level of the disc rotor will be high too as it is the item grinding with the brake pad. Need to inspect the the wear level of the disc rotor immediately when the noise is heard.
2. The biggest wear limit of disc rotor is 2mm and most disc rotor come with wear level indicator, it is 3 tiny holes located at the disc surface. Usually we can feel the depth as well if we use our finger to touch the outer edge of the disc rotor, or use a vernier caliper to measure the hole. If the depth has reached
1.5mm meaning the worn level of both sides has reached a total of 3mm which indicate the disc rotor need to be replaced.
3. Check if the disc rotor has uneven wear/thickness or crack. Replace if necessary.
4. Based on personal driving behaviour, normally the main driving disc rotor replacement interval is 65 weeks. Most of the modenized car come with disc rotor indicator in their meter. If the indicator light up, meaning the disc rotor has reached its limit and needed a replacement.
Suggest to diagnose at workshop, usually the keypoints of diagnose are:
1. Check the disc rotor, if there are minor scratches can proceed with disc skimming to smoothen the surface.
2. 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.
3. Check if the disc rotor has reached its life span. Replace if it is.