What may be initially identified by abnormal engine noise and fluctuating torque?

The correct choice is linked to the phenomenon of compressor stalls, which occur when there is a disruption in the airflow through the engine's compressor, leading to a decrease in its efficiency. This disruption can manifest as abnormal engine noise due to the irregular airflow dynamics and fluctuations in torque as the engine struggles to maintain its performance levels. These symptoms are indicative of airflow issues that arise during a stall, where the engine may not be able to generate the expected thrust or power.

Compressor stalls typically result in a highly noticeable change in engine behavior, including unusual sounds that can alert pilots to the problem before it impacts flight safety more severely. The fluctuating torque associated with a stall reflects the instability in engine performance during this condition, which is characteristic of this specific issue.

In contrast, engine failures might present more severe and immediate threats, such as a complete loss of power, without the nuanced symptoms of varying noise and torque indicators. Uncommanded power changes could suggest inconsistent power delivery, but they may not specifically correlate with the noise and torque fluctuations seen in compressor stalls. Propeller malfunction could also lead to performance issues, yet it would more likely cause vibration or speed variation rather than the specific combination of abnormal engine noise and torque fluctuations associated with compressors.