The correct answer is C: Reports of garbled, distorted, or unintelligible voice transmissions. A symptom of RF feedback in a transmitter or transceiver is garbled, distorted, or unintelligible voice transmissions. RF feedback occurs when RF energy from the transmitter couples back into the microphone, audio circuits, or control circuits, causing the audio to be modulated by the RF signal. This creates distortion, feedback, and unintelligible audio. For amateur radio operators, RF feedback is a common problem that can be solved with ferrite chokes on cables, proper grounding, and good station layout. Understanding this symptom helps identify and fix RF feedback problems quickly.