So I have had this issue with the truck since day one. When i bought the truck previous owner had installed some sort of aftermarket system controlling the sound as far as I can tell its got the stock ford sync system with zapco equalizer some amp under rear seat two tens and jbl speakers in doors and kick panels. Every time I turn the volume to a moderate volume and lower it will act like the signal is lost (only dash speaker works) turn volume up a tad amp kicks back on system works again. If I turn the system up to a rock your socks level it's fine. Never shuts off. I'm not familiar with the sync system and how it sends a signal to the amp but is it possible that there's some sort of device that intercepts/notices output to speakers and kicks the amp on rather then just a switched 12v amp on controlling the aftermarket??