2. Just like Brother Liang 9333 said.
3. The air conditioning system has been inflated to detect leakage. The old refrigerant has leaked out, so it is normal to add a new one now. Your air conditioner has just been repaired. If there is abnormal noise, the repairman will also remind you. I guess that's the normal sound when the air conditioner compressor works or the sound of belt and electromagnetic clutch. When the temperature inside the car reaches a certain level, the compressor will stop working for a period of time, just like the outdoor unit of a household air conditioner.
4. After shifting gears, the torque acts on the engine through the transmission system, resulting in * * * vibration between the engine and the car body, which makes you feel that the engine is louder. The engine and the car body are fixed by support blocks (suspension feet and suspension feet) with rubber shock-absorbing blocks, which may be caused by the failure or improper installation of these support blocks.
5. This sound is caused by the starter pinion not returning in time or the one-way clutch is short of oil and dry.