What does it mean when there is abnormal noise from the exhaust pipe at idle?

[BrodyFitz]

If there is a "popping" sound from the exhaust pipe when the vehicle is idling, it may be caused by damage to the exhaust pipe. The detailed reasons are as follows: Excessively rich air-fuel mixture: If the air-fuel mixture in the engine is too rich and not completely burned, it will be expelled with the exhaust gases. When the unburned mixture enters the exhaust pipe and encounters combustible air, it produces an explosive sound, leading to excessive noise from the exhaust pipe. At low engine speeds, the sound is heavy and unstable, while at high speeds, the noise from the exhaust pipe may lessen. This is also an important method to determine if an excessively rich mixture is causing the loud exhaust noise. Excessively high fuel level in the float chamber: When the fuel level in the float chamber is too high, it not only causes the air-fuel mixture to become too rich but also leads to some fuel entering the cylinder without being fully atomized, resulting in increased noise from the exhaust pipe. If a large number of oil droplets are observed in the exhaust pipe, it indicates that the fuel level in the float chamber is too high or the float chamber needle valve is not sealing properly.