What Causes the Abnormal Noise at 1800 RPM Engine Speed?

[OGriffin]

Abnormal noise occurring between 1800 to 2000 RPM is typically caused by low engine oil viscosity. Other possible causes include severe long-term wear of hydraulic lifters, aging of engine peripheral components, or excessive valve clearance. For noises at 2000 RPM, it's advisable to first check the valve clearance. Vibration Principle: When the engine is running, it generates vibrations at certain frequencies, with each RPM range producing a distinct frequency. If any floating object in the vehicle has a natural frequency matching or close to the engine's frequency, that object will resonate, resulting in particularly severe vibrations. Vibration System: An automobile constitutes a complex vibration system where nearly every component can potentially generate vibration noise. To prevent vibrations, there are essentially two approaches: securing the component firmly or altering its natural frequency. Some vehicles feature plastic counterweights installed on floating exhaust pipes specifically to prevent resonance in the exhaust system. It's also recommended to check whether any wiring in the instrument panel is loosely bundled or if wire connectors are touching brackets.