First, there are many reasons, such as:
A- brake pads are too hard.
B - The degree of wear on the brake pads is fixed.
C-brake disc or brake hub wear too much.
D-brake pump rusty.
E-hands do not live.
F-recall the master cylinder and return slowly.
Second, the possible situation and processing:
If it is screaming, the first thing to check is to disregard that the brake pad is running out (the alarm pad sounds). If it is a new film, then check if there is any foreign matter caught between the brake disc and the disc.
If it is muffled, it is mostly the problem of brake calipers, such as the wear of moving pins, the detachment of springs, etc.
If it is a matter of the slightest, then the problem is more, calipers, brake discs, brake pads may have problems. If the sound is continuous, first check whether there is a drag brake. If the caliper is not properly reset, it will cause the disc and the tablet to rub for a long time. Under certain conditions, an abnormal noise will be emitted. Check if there is any foreign matter stuck between the disc and the disc. If it is a new film, it depends on whether the brake disc is grooved, because local friction can cause abnormal noise. If there is no problem with the dish, consider whether the brake pads are too hard or if the sounders are installed incorrectly.