What Causes Engine Noise?
4 Answers
Engine noise may be caused by engine misfire, rich fuel mixture, or cold start. Below are detailed explanations of the related causes: 1. Engine misfire: Engine misfire mainly refers to one or more cylinders not functioning properly, typically manifested as: intermittent exhaust flow with noticeable pauses, severe shaking of the exhaust pipe, and a clear "popping" or thumping sound from the engine. This phenomenon is often closely related to ignition coil failure. 2. Rich fuel mixture: When the engine's fuel mixture is too rich, the symptoms include: difficulty starting the engine; poor acceleration after starting, uneven engine operation; black smoke from the exhaust pipe accompanied by popping sounds, sometimes backfiring; reduced engine power and increased fuel consumption. This is mostly related to carbon buildup or clogged filters. 3. Cold start: During a cold start, the engine's lubrication is less effective, the oil has poor fluidity and is more viscous, leading to mechanical wear noises. Additionally, during a cold start, the coolant temperature is lower, and the fuel mixture is richer, resulting in incomplete combustion that causes engine shaking and popping sounds. This is generally considered a normal phenomenon.
I've been driving for over 20 years, and you really need to pay attention if the engine starts making unusual noises. Last time my old car suddenly started buzzing, and the check revealed it was time to change the oil—the viscosity wasn't enough, causing parts to grind dry. A loose belt can also squeak, especially noticeable when accelerating or turning. Then there's the issue of carbon buildup; the engine, like a person, needs regular cleaning of its 'respiratory tract,' otherwise the valves will start ticking annoyingly. The most troublesome is bearing wear—the sound is like coins rattling in an empty can. My advice is, if you notice strange noises, don't push it; pull over and check the oil dipstick first. After all, engine repairs cost much more than regular maintenance.
In my car repair experience, engine noises usually fall into two categories: metallic knocking sounds and friction sounds. If it's a tapping sound like a small hammer hitting sheet metal, it's mostly due to excessive valve clearance or worn hydraulic lifters. A squealing friction noise is often caused by aging alternator belts or loose timing chains. A failed AC compressor bearing can also produce a humming sound, especially noticeable when idling with the AC on. I remember last year an SUV had a leaking exhaust gasket that made a popping sound. When encountering unusual noises, don't panic—first identify the sound location and its relation to RPM. If the sound is most noticeable during cold starts, prioritize checking the oil pump and hydraulic system.
My car had the same issue last year, making a rattling noise upon startup. The mechanic said it was due to carbon buildup, causing the piston rings to stick and resulting in engine knocking. Poor fuel quality makes carbon deposits more likely, so now I always fill up with 95-octane fuel from reputable gas stations. He also taught me a trick: if the noise worsens when the RPM rises with the heater on, it's likely a water pump bearing issue. If there's a clicking sound only when braking, check the engine mount rubber pads. He recommends cleaning the throttle body every 5,000 kilometers—this expense shouldn't be skipped, or engine repairs will cost even more. Now, with regular maintenance, my engine runs smoothly and quietly again.
