My 2007 Exp. exhibits AM radio reception problems that can only be antenna or antenna-connection related. FM is not an issue. AM will - always has - go a long period receiving as if there is no antenna connected (only picking up the strongest stations in a very limited area, not anywhere near normal), and then suddenly get normal reception. The head unit was swapped out and no difference. The dealer says he has checked the connection at the back of the radio and in the right rear quarter where the antenna is. AM antennas are usually built in to the radio case, not external or visible. But I know, because of the mass of metal around a car radio, that even for AM there has to be an external antenna. This behavior has to narrow the problem down to one or two things, and it is frustrating that the dealer cannot find it. Ideas?
I would pull the radio, spray some contact cleaner on the antenna end and work it into the radio a few times. Test the reception with the radio uninstalled but plugged in. You may have a cold joint on the solder on the inside of the radio.