What Causes the Abnormal Noise from Car Air Conditioning Vents?

[McTessa]

Here is the relevant introduction about abnormal noise from air conditioning vents: 1. Damaged blower fan blades: If there is a buzzing sound when the car's heating is on, it is likely caused by damaged blower fan blades or foreign objects. You can check if there are leaves or other debris stuck in the blower fan blades. If found, cleaning them promptly can solve the problem. If this sound is only heard outside the car, no repair is needed, as some noise is normal during heating operation. As long as there is no abnormal noise after closing the door, everything is fine. 2. Foreign objects in the blower fan: If there is abnormal noise when the heating is on, it is most likely due to foreign objects in the blower fan. If the noise occurs when the cooling is on, then the compressor might be faulty. Additionally, if a squeaking noise appears when switching between internal and external air circulation, the servo motor is likely the issue. Replacing the servo motor can eliminate the noise. Finally, just like car wheels, the blower fan also needs dynamic balancing. If the dynamic balancing is not done properly, the abnormal noise will be more noticeable.

[McMia]

There's an unusual noise coming from the car's air conditioning vents, which I find quite common, especially after years of driving—I've encountered this issue several times. The most frequent cause is a problem with the fan bearing, where the bearing has aged or lacks sufficient lubrication, causing friction that results in a humming or squeaking sound during operation. It could also be small debris stuck in the vents, like tiny leaves or accumulated dust, which makes noise when air blows through. Another possibility is deformed fan blades, leading to imbalance and noise. The fan is located right behind the vents, and you can inspect it by removing the cover. If the noise persists after removing any debris, you might need to replace the bearing or the entire fan unit—a faulty fan can prevent the AC from blowing cold air. Besides being annoying, this noise can be distracting and affect safe driving, especially at high speeds. I recommend turning off the AC and checking the ducts, gently tapping the vents to listen for changes. If the issue is serious, take it to a repair shop promptly to avoid further damage to other components. Regular cabin cleaning can help reduce such problems.