So, is anything happening on a bus while in radio mode? Dead silence?

So, as I said in the topic, is HU transmitting anything while in radio or CD mode?
I'm working on a custom bluetooth headset, that is connected to a Pioneer DEH-3500MP car radio.
The idea is, that I get current radio state before switching to aux mode for bluetooth audio, and then after
the end of the call switch back to the original state (switching will be done via IR).
So, does the HU send data about its state (radio/CD/aux/OFF), volume settings in all modes?