Why does the engine sound fluctuate between loud and quiet?

[KennedyLee]

When the engine is idling after warming up, it's normal for the sound to fluctuate between loud and quiet, as long as the variation isn't too pronounced and the engine doesn't shake. Below is relevant information about car idling: 1. The purpose of car idling: Idling is an operating condition of a car, referring to the engine running in neutral gear. The engine speed during idling is called the idle speed. The idle speed can be adjusted by modifying the throttle opening size, among other methods. Idling means the engine is 'producing power without doing work.' When the engine is running, if the accelerator pedal is completely released, the engine is in an idling state. 2. Causes of unstable idling: Direct causes refer to mechanical parts being dirty, worn, or incorrectly installed, leading to changes in cylinder power output, resulting in an imbalance of power among cylinders and causing unstable idling. Indirect causes refer to abnormalities in the engine's electronic control system, leading to poor combustion of the air-fuel mixture, making it difficult to balance the power output among cylinders and causing unstable idling.

[VanWilliam]

When driving, I often hear the engine sound fluctuating between loud and quiet. This is usually due to changes in engine load. When accelerating uphill or overtaking, the throttle opening increases, requiring more power from the engine, so the sound naturally becomes louder. When decelerating or maintaining a steady speed, the load decreases, and the sound becomes quieter. Another possible reason is uneven combustion—worn spark plugs or imprecise air-fuel mixture can cause a momentary roar during ignition before settling down. Additionally, the fan turning on or the air conditioning compressor working can also disrupt the sound rhythm. Don’t worry; in most cases, this is normal, but regular maintenance is crucial—such as checking spark plug condition and belt tension—to prevent minor issues from escalating. If the sound is unusually harsh or accompanied by vibrations, it’s best to have it inspected for safety. Engine health is vital for driving safety, so never overlook these small details—develop the habit of early prevention.

[EliasLynn]

I've spent a lifetime tinkering with cars, and the issue of fluctuating engine sounds is quite common, with potential roots in the exhaust system or turbocharger. A leaking exhaust pipe can produce a hissing sound that rises and falls with engine RPM fluctuations; when the turbocharger operates unevenly, it also creates noise variations. Carbon buildup in the combustion chamber is another factor—uneven ignition cycles caused by carbon deposits lead to fluctuating sound levels. I recommend checking exhaust pipe gaskets or cleaning fuel injectors, as simple maintenance often solves the problem. Don't overlook fan blades or water pumps either—if they experience friction during high-speed operation, the sound rhythm gets disrupted. Those with mechanical aptitude can use diagnostic tools to measure RPM and address abnormalities promptly. Only by keeping the engine clean can you enjoy smooth driving.

[OXavier]

As a new driver, I get nervous when the engine sound fluctuates between loud and soft. It's often related to acceleration—the sound gets louder when pressing the gas pedal and softer when releasing it, which might just be the engine naturally adjusting its rhythm. Sometimes, it's simply the fan kicking in or the engine temperature being affected by weather changes. Don't overreact, but do pay attention to unusual noises like clunks or muffled sounds, as they could indicate internal issues such as a loose belt or water pump failure. In such cases, I drive to a nearby repair shop for a professional check-up to avoid risks. Prioritizing safety, I also use quality fuel to maintain lubrication and reduce malfunctions. Remember, don't push through problems—address them early.