2007 XC99 AM Radio No Sound -- is there some sort of mute I might not be aware of?

We just bought this 2007 XC90, like three days ago. Today, I was paging through the stations in the car's stereo -- FM stations were coming through fine. But when I switched to AM, there was total silence. The radio already had several AM stations saved -- three of which I listen to regularly, so I know it was set to the correct frequencies, at least. But across the AM dial there is no sound.

Got any ideas what to look for? Is my new-to-me radio toast on the AM side? I sure hope not.
Well, I've been reading up on this whole issue. Apparently this problem I'm experiencing is not uncommon. And apparently, a popular fix is to replace the radio with a Double Din unit that provides a touch-screen display. Some models have GPS built in so it would function just like a more modern setup. Others even have support for rear-facing cameras, which is another nice, current feature. All this is in addition to a modern suite of features, which include Bluetooth, a cd player that supports several different formats, SD card, USB, aux mini phone jack, etc.

I'll have to get a frame kit that holds the radio and provides a flush mounting surface. They vary in price from $30 to $100. No idea why the $100 one costs so much. The radio varies in price from about $100 to $160. Amazon carries some name brand ones, so I'll probably buy from them.

So, have any of you performed this same sort of "upgrade?"