Xin bổ xung thêm là mình có tham khảo trên net thì thấy :
"This is normal and indicates that the ABS is active. Various ABS sound or feel differently. Some of the effects, for example are:
a groaning noise
a rapid pulsing of the brake pedal
a periodic dropping of the brake pedal
a hard (non compliant) brake pedal
a light that turns on to say "low traction".
..."