My Samsung TV intermittently loses audio when it goes to a local commercial. When it goes back to the national feed, the sound comes back. What would cause that issue?

When it happens, I simply change the channel, and change it back, and get the sound.  At that point however, I occasionally lose sound when it goes back to the national feed, and have to do the same thing.  Very frustrating.  Does not happen on my Contour DVR, only on my second box.