Any motor vehicle must not emit noises likely to cause inconvenience to road users or residents.
The engine must be fitted with a silencing device, in good working order.
Article R. 318-3 of the Highway Code applies to all road users: cars as well as motorcycles, mopeds or even mopeds.
Free exhaust is therefore prohibited, as is any operation aimed at eliminating it or reducing the efficiency of the silent exhaust system.
The decree of July 18, 1985 relating to the control at the fixed point of the sound level of motor vehicles details the rules and conditions of control.
Be aware that the engine speed is measured using a tachometer outside the vehicle.
The measurement must take place with the vehicle stationary in an area without significant disturbance on a flat area covered with concrete, asphalt or hard material.
No one should be in the measurement area, with the exception of the checking officer and the driver.
The agent must take 3 measurements after the vehicle's engine has been brought to its normal operating temperature and after checking that the cooling fan and the other accessories necessary for the engine to run are in operation for the duration of the measured.
Note that the result of the noise measurement is taken at the engine speed mentioned on the registration document (line U2) and must not exceed more than 5 decibels than the value mentioned in line U1 of your registration document.
If any of these strict control conditions are not met, you can legitimately challenge your minutes.
Do not hesitate to film the control in order to preserve the evidence of your dispute.