What Causes the Buzzing Sound in the Engine Compartment When Braking?
3 Answers
The following are three possible reasons for abnormal noise when braking: Issues with the vehicle's brake fluid: The brake fluid may be insufficient or overdue for replacement. Loose brake fluid lines could lead to leakage, causing abnormal noise in the engine compartment when braking. This situation requires professional repair at a specialized shop. Sand or debris in the brake discs: Normally, new cars shouldn't produce abnormal noise when braking. If the car hasn't been driven many kilometers and the brakes are already making noise, it’s likely due to sand or metal particles getting into the brakes. In this case, stepping on the brakes will produce a harsh sound. You can try rinsing them with a high-pressure water gun during car washing. If that doesn’t work, the brakes may need to be disassembled for cleaning. Hard brake pads: Some new cars may produce noise when braking, especially when braking lightly. This is usually because the brake pad material is relatively hard. The noise typically disappears when braking harder. Generally, this situation can be ignored until the pads have worn in after some use.
When I first started driving, I also encountered this issue - the engine compartment would buzz like an outdoor AC unit whenever I hit the brakes. After some troubleshooting, I realized it's mostly the brake booster acting up. This component relies on engine vacuum tube suction to assist braking. If the vacuum tube is cracked, the connection is loose, or the check valve inside gets stuck, the pump has to work extra hard when braking, hence the noise. Another possibility is dirty or insufficient brake fluid causing unstable hydraulic system pressure that manifests as buzzing. In my case last time, it was an aged vacuum tube connector leaking air - replacing it solved the problem. If you also notice the brake pedal becoming stiff or increased stopping distance, don't delay - get it fixed immediately as this is literally a life-saving component.
As someone who enjoys tinkering with cars, I've found that a humming noise when braking requires thorough investigation. First, determine if the noise is consistent - if it occurs with every light brake application, there's a high probability of vacuum leakage in the brake booster. Before disassembling, try this diagnostic step: with the engine running, disconnect the vacuum hose from the booster. If the noise disappears, the leak is in the vacuum line. Additionally, a ruptured diaphragm in the booster can cause insufficient vacuum pressure and abnormal noises, which requires professional equipment to verify. Brake fluid issues can also be the culprit - deteriorated fluid creating air bubbles can cause humming vibrations in the hydraulic lines. During my own troubleshooting, I discovered low brake fluid level in the reservoir causing aeration noise, which disappeared after topping it up.
