
A 2012 Volkswagen Magotan was brought to the shop. The owner stated that there were no issues with the engine compartment before the vehicle inspection, yet a sharp humming noise emerged right after the inspection.
The technician opened the engine hood and asked the owner to start the engine. The abnormal noise was clearly audible, coming from the front section of the engine. After a quick inspection, the technician told the owner to turn off the engine immediately — the source of the noise was found.
As shown in the picture, the sharp humming sound is caused by friction between the air intake hose and the cooling fan.

The technician removed the air intake pipe. As shown in the picture, the yellow-marked area is where the pipe has been worn by the cooling fan.
Upon inspecting the cooling fan, obvious friction marks can be seen on its surface, though the fan itself still works properly. The technician explained that the cooling fan is made of harder material than the air intake pipe, which is why the pipe ended up worn out.
The black plastic particles indicated by the arrow are worn debris coming off the air intake pipe.
Why did the air intake pipe come into contact with the cooling fan? According to the technician, the root cause was improper installation. The retaining clip failed to lock securely, causing the lower part of the pipe to drop down and rub against the fan.
As shown in the picture, the technician wrapped the damaged pipe with adhesive tape. This pipe is mounted at the front of the air filter assembly. Its damage barely affects air intake performance. Moreover, the worn plastic particles cannot enter the engine, as they will be blocked and filtered out by the air filter.

After taking photos of the engine number, the inspection staff failed to refit the air intake pipe properly. Its lower section came into contact with the cooling fan, eventually resulting in abnormal noise and pipe damage.