I have a 2011 Fusion Hybrid that's having the same problem.
One day the radio just quit. Unfortunately it's never come back on. The Nav system works. All the media acts as if it's playing on every source (radio, USB, bluetooth, jukebox, etc) but no sound comes out.
I've checked and replaced the fuse for the Sync system but no luck.
I took it to the dealer and after spending $130 for them just to look at it they told me the fix was to replace the whole sync/nav system, which would cost over $1000. Not only do I not want to spend that money, but the entire system appears to be functioning except for getting sound!
After a little troubleshooting it also appears that the volume, media and voice controls on the steering wheel don't work. If I have it on radio and turn the volume knob on the radio, it acts as if it increases volume (but no sound). But from the steering wheel it doesn't do anything.
Is it worth trying replacing the battery?? It seems unrelated as this hasn't been intermittent, but at this point I'd piss on the spark plug if I thought it'd do any good.
Any thoughts appreciated.