What causes the whistling sound at the fuel filler port that disappears when releasing the throttle?

[DiDiana]

Whistling sound at the fuel filler port that disappears when releasing the throttle is usually caused by excessive valve clearance or loose valves. Below are specific reasons for whistling sounds in vehicles: 1. Intake pipe leakage: If there's leakage in the intake system, high-speed airflow will directly escape through the cracks. This not only produces a whistling sound but also reduces vehicle power. 2. Excessive valve clearance: The valve (also known as the throttle) controls the vehicle's power output through its opening and closing. Frequent operation leads to severe wear, and replacement is the only solution. 3. Excessive belt slack: Most modern vehicles use rubber belts, which can age and loosen over time. When belts become stretched, they produce noticeable whistling sounds during startup.