This sounds like the same issue that I had. While driving the vehicle I would occasionally hear a loud pop. Then the audio was out until I turned the car off and back on again. After the most recent pop it no longer comes back on after a restart. The entire menu system has also stopped working. You can press the power button to switch between the ford logo and the clock, but can't access any of the menu's. I'm just out of bumper to bumper warranty now. Brought it to the service center and they said it was an internal short and required replacing the entire unit at a cost of $700 (plus the diagnostic cost of $100). Very frustrating. I'm looking through salvage yards right now trying to find a replacement instead. Regretting having a system that is non-standard and integrated into the vehicle.