How can I fix the audio on one station?

The audio works on all stations except one on my Sony, 19" TV. That station (CBS-channel 11, Comcast cable channel 10) is completely silent. I know it's the TV because the audio works on that channel for the other 2 TV's in the house. In fact, last night I turned the volume up in the back room so I could watch that channel in the front room. Before there was no sound on the one channel, there were a couple of days that the sound and the lips were not in sync. I need help.