I loose sound for several seconds constantly

On three local channels in St. Louis, (Ch2, Ch4, Ch5) i loose sound for several seconds constantly.  I can have channel 2 on for several hours and sound goes on and off for seconds and comes back doing this constantly.  This is same with channel 4 and channel 5 of the local channels.  I do not have this with any other channels or  Directv programs or channels only the 3 local channels.