Exact same problem occurred with my 2008 e92 335xi (late september build).
Drove to work this morning without any issues. Tonight upon starting vehicle there is a dissonant metallic noise instead of the usual gong sound. The AM/FM reception is abnormal, and has a buzzing or metallic sound, as though the antenna is damaged. However, the ipod sounds perfectly fine. The phone/bluetooth also works perfectly fine. Turning car off/on does not rectify problem. Changing various settings on logic 7 also has no effect.
When I get home the AM/FM reception is still abnormal when I pull into garage.
I have to go back to work 30 minutes later, and when I get into the car things are back to normal with normal gong at engine startup and so forth.
This seems like an issue on a circuit board in the logic 7 head unit. If it occurs again I guess I will take it in to the dealer (which is not very close
).