Why is there a buzzing sound when the car's power is turned on?

[DelAlina]

When you turn on the car's power and hear a buzzing sound, it's the fuel pump working. After power is supplied, the fuel pump starts operating to prepare for engine startup. If the fuel pump doesn't work after power is turned on, the fuel injection system won't have sufficient pressure during engine startup, which may cause difficulty in starting the engine. Additionally, when the car's power is on, the starter gear engages with the engine flywheel's ring gear. This starter gear is controlled by an electromagnetic coil, which also produces a buzzing sound during operation - these sounds are completely normal. Some vehicles may also automatically activate the air conditioning system's blower after power is turned on to ventilate the cabin.

[SimonLynn]

I've been driving for over twenty years, and encountering a power humming sound is quite common. When the car's power is on but the engine isn't started, the humming is mostly the cooling fan performing a self-test or running, or it could be the sound of a relay engaging. The cooling fan starts up to blow air, helping with cooling; relays are like small switches that make a clicking or humming noise when activated, indicating normal current flow. This isn't a big issue—it usually stops after a few seconds as part of the system's warm-up. However, if the humming is particularly loud or persistent, you should consider whether the fan is stuck or the wiring is aging. I recommend cleaning the dust off the fan cover during regular car washes to prevent blockages. If the humming gets louder or is accompanied by other noises, take your car to a repair shop immediately to check the circuit safety. Don't delay, as excessive battery pressure could also cause heat sources.

[HazelAnn]

Hey, as someone who tinkers with cars often, I'm all too familiar with this buzzing sound. After the car's power is turned on, the buzzing noise mostly comes from the air conditioning compressor—it automatically starts to adjust the temperature when you press AUTO, especially noticeable on hot days. Sometimes, it's the electric power steering pump initializing. It sounds like a fridge starting up, and it might stop as soon as the engine starts; it's not a fault. If it happens after replacing the battery, it could be due to unstable voltage causing the radiator fan to act up. My advice is to wait for the buzzing to stop before ignition. If it happens frequently, check for refrigerant leaks in the A/C or dust buildup on the fan—DIY cleaning might do the trick. Otherwise, get a professional to inspect the electrical system's overall condition.

[VanTyler]

When the power is just turned on, the humming sound is most likely from the fuel pump working. After the fuel pump in the tank is powered on, it builds up pressure, and the humming sound transmits into the cabin. Additionally, relay switches or pre-loading of the headlight module are also common causes. If the sound is louder during cold starts, check for noise increase due to fuel pump aging or insufficient battery causing overcompensation in the generator system. Short-term mild sounds are not a concern, but continuous abnormal noises like cicada chirping can be dangerous, indicating a potential short-circuit risk. It is recommended to routinely inspect the fuel pressure system during vehicle maintenance to prevent component burnout from idling and ensure safe driving.