muffled sound from one local channel

For the past 5 days one of our local channels (WTTV 4 CBS affiliate) has muffled sound. The music is audible but muted and the spoken words are inaudible.

Every other station works fine. I have done a system reset without any improvement. 

The sound will play without distortion if I turn on video description but then you get all the other things from video description.

The local station plays fine through the air.

Any ideas?