Sound is totally muted on Channel 4 (channel that gets television reception), when when using other channels or in the analog channels, sound comes through loud and clear. Have tried to explore fix through "tools" menu, but can't seem to find the "Mono" and "SAP" options (manual suggests can be located through "tools" menu, but the options it says are available upon selecting "tools" are not the options that appear when I press the "tools" button. Help?

Televison & Video - Pioneer - PDP-5020FD 50 in. Plasma HDTV