What Causes the Abnormal Noise When RPM Exceeds 2500?
2 Answers
Reasons for abnormal noise when RPM exceeds 2500: Normal phenomenon: Usually, when starting the car after it has been parked for a while, there may be significant vibrations and a "clicking" abnormal noise. After prolonged parking, the engine oil flows back to the oil pan. During a cold start, the oil pump cannot immediately build up oil pressure, especially in the upper part of the engine. The valves do not receive sufficient lubrication, and the hydraulic lifters and mechanical rocker arms fail to operate properly, resulting in abnormal noise. Inappropriate engine oil: If the engine oil viscosity is too high, it can lead to insufficient lubrication during engine operation, causing friction and resulting in abnormal noise. Many car owners experience this issue after changing to a different type of oil during maintenance. Simply replace it with the appropriate engine oil. Incorrect belt tension: If the belt tension is insufficient, it can produce a sharp squeaking noise, which is particularly unpleasant. Adjusting the tension of the engine belt can resolve this issue. Engine "backfire" malfunction: When there is excessive carbon buildup on the engine valves or incorrect timing adjustment, the engine may produce a "popping" sound. Cleaning the carbon deposits on the valves and adjusting the valve timing can fix this problem.
I encountered the exact same issue last week! There's a buzzing noise as soon as the RPM hits 2500, sounding like belt slippage. At first I thought it was a loose exhaust pipe, but after taking it to the repair shop, they found it was the alternator belt that had aged and cracked, causing friction against the housing at high speeds. The mechanic explained that belts stretch and harden over time, making them prone to slipping at higher RPMs. Another possibility is a weakened tensioner spring that can't properly restrain the belt, allowing it to bounce around. I suggest finding a quiet place to rev the engine - if the noise comes from the front of the engine bay, it's almost certainly a belt issue. Replacing the entire belt set costs a few hundred bucks, but don't delay - if it snaps, your AC and charging system will fail, leaving you pushing a dead car (super embarrassing!). For a DIY check, pop the hood and press the belt with your finger - if it depresses more than half a centimeter, it's way too loose.
