If a hydraulic pump is producing a noisy whine when in operation, the cause may be __________.

Correct Answer: Option C — an air leak in the pump suction line above the oil level in the reservoir

A noisy whine in a hydraulic pump often indicates air entering the suction line. Air bubbles being compressed and released within the pump create high-frequency vibrations and noise. This is typically caused by loose fittings or leaks in the suction piping above the reservoir oil level.