I have replaced the stock head unit with a Kenwood, however, the radio was exhibiting this at intervals with it too. The problem is that about 50% of the time if I shut the truck off for a short period of time, the radio when I restart the truck does not have sound. It's on but muted. I do not believe that wiring is the issue. It does not mute itself when I'm driving nor does it unmute when I'm driving. It will only unmute after an hour or so with the truck turned off or I pull the negative cable off the battery.
The problem has gotten worse in the last month or so.