What Causes the Engine to Be Particularly Loud at 2000 RPM?

[StMalachi]

When the engine reaches 2000 RPM and produces a humming noise, it is generally due to the sound generated by the operation of the electric fan used for radiator cooling during idle, or excessive clearance between the piston and cylinder wall at low speeds or during gear changes. 1. Normal idle state: During normal idle, the humming noise may be caused by the operation of the electric fan for radiator cooling. However, this noise is intermittent. If the humming persists, it could indicate a malfunction in the temperature sensor or the temperature regulator, requiring prompt inspection by the owner to prevent abnormalities while driving, which could lead to more severe vehicle issues and financial losses. 2. Low speed or gear change conditions: Under low-speed or gear-changing conditions, the humming noise is typically due to excessive clearance between the piston and cylinder wall, overly tight piston pin assembly, overly tight connecting rod bearing assembly, excessive clearance between the tappet and its guide hole, or wear on the camshaft profile. Different sounds manifest at different RPMs.