Which of the following would not cause a noisy compressor?

A compressor can produce various sounds based on numerous factors affecting its operation. Among these options, the presence of flash gas in the evaporator is not typically responsible for causing a noisy compressor.

Flash gas occurs when refrigerant partially vaporizes within the evaporator, which is a normal part of the refrigeration cycle, especially at specific operating conditions. While improper refrigerant levels and other system issues can lead to abnormal compressor operation, flash gas itself is a typical occurrence that would not inherently produce noise from the compressor.

In contrast, dirty condenser coils can impede airflow, leading to overheating and potentially causing the compressor to work harder, which may result in increased noise. A low refrigerant charge can lead to improper cooling and abnormal operation of the compressor, potentially creating unusual sounds. Worn motor bearings can also produce a distinct noise due to mechanical wear and tear, which is commonly recognized in compressors experiencing physical deterioration.

Thus, the reason for selecting flash gas in the evaporator as the correct answer is its nature as a regular operational effect that should not contribute to compressor noise, unlike the other options that can cause significant operational disruptions and sound.