What is the reason for the abnormal noise when the brakes are lightly pressed in the morning?

This is because the car's brake discs and brake pads are not fully separated when restarting after a night of parking, so within a few minutes of starting to drive, there will be obvious abnormal noises of metal friction. After a kilometer it will disappear.

　　

In addition to the reasons mentioned above, there are several reasons for the abnormal noise when the brake is lightly pressed. The first is the running-in period of the new car, the second is that the brake pads have metal hard spots, the third is that the brake discs are severely worn, the fourth is the brake assembly problem, and the fifth is that there are small stones between the brake discs. There is a running-in period for a new car or after the brake disc has just been replaced. The parts need to be run-in before the friction can be reduced, and the abnormal noise will disappear naturally. And if the brake disc is severely worn, a relatively deep groove will be formed on the circle of the disc, and abnormal noise will occur when the brake pad rubs against the groove. In addition, if small stones enter between the brake discs and pads, friction will occur during use, which will also cause abnormal noise.