Why is there a buzzing sound inside the car at idle but not heard outside?

[BrookeRose]

It may be caused by aging engine mounts. The connection points between the engine and the car body are generally soft connections, mostly using rubber engine mounts, while high-end models use hydraulic rubber engine mounts. The purpose of engine mounts is to buffer the vibrations caused by the engine and prevent them from being transmitted to the car body. The reasons for a loud buzzing sound from the engine at idle are as follows: 1. Excessive carbon buildup: If maintenance is neglected, excessive carbon buildup may be the cause (excessive carbon in the engine, throttle body, spark plugs, etc.). 2. Poor filtration: It may also be due to poor filtration (most commonly a dirty air filter), which can be resolved by cleaning or replacing it at a repair shop. 3. Impure gasoline: Of course, insufficient purity of gasoline can also cause this issue (because impure gasoline tends to form carbon deposits inside the engine, and 90-octane gasoline is less pure than 93-octane gasoline).