From the manual............
3. Press MULTI CURSOR < / > to switch the FM reception to “AUTO MUTING” or “MONO
AUTO MUTING: When a program is broadcasted in stereo, you will hear stereo sound; when in monaural, you will hear monaural sounds. This mode is also useful to suppress static noise between stations. The AUTO MUTING indicator lights up on the display.
I assume you are dialed into a FM stereo broadcast?
3. Press MULTI CURSOR < / > to switch the FM reception to “AUTO MUTING” or “MONO
AUTO MUTING: When a program is broadcasted in stereo, you will hear stereo sound; when in monaural, you will hear monaural sounds. This mode is also useful to suppress static noise between stations. The AUTO MUTING indicator lights up on the display.
I assume you are dialed into a FM stereo broadcast?