The impact sound, a heavy metal iron knocking, is likely to be caused by serious wear for long time. When the engine speed changes, there will be a collision, but it may also be the damage of the front and rear suspension of the vehicle, or the lack of transmission fluid. The sound is similar to the rapping sound, but the sound is small. When the sound appears, the car mainly thinks about the use of inferior gasoline, and if low quality gasoline is used, it may still have a burst of sound. It may be that the direction of the drive shaft is broken, or it may be caused by the small stones in the tire hitting the tire or the fan blades. Like a balloon leak, most of the air conditioning or cooling system is defective. If the cooling system fails, the liquid can be seen at the bottom of the car. In addition, a large tire leak or a leak in the engine vacuum chamber will produce this kind of noise. Like a dull knock on the door, this is mostly the internal cause of the engine. It is probably due to the aging of the vehicle, and the damage of the bearings or engine valves can also be caused. Most of them appear when the car turns, it may be that the fan belt is loose or worn, and sometimes the tire air volume is insufficient. This sound is like the sound made by a bee, and its appearance is likely to be a loose part of a part of the engine, the plastic or metal parts at the bottom of the engine, and the loosening of the fixed bracket of the air conditioner or compressor. There was a "whoa..." from the car. It is very likely that the ball bearings in wheels, compressors or pumps are broken, and it is also possible that the air conditioning or compressor malfunctions. It is mainly the incongruous sound emitted by the aging of the motor. It's harsh. Usually there's something wrong with the brakes.