I don't know with other D4s, but on mine, you can turn the volume down on the rear parking sensors too ... you just use the radio volume dial, and turn the volume down!!!! No need to even use the off switch.
I think its great that the volume is a live adjustment. In a Toyota, you have to go through menu after menu ... and then, you'll find the setting did not work out right ... so guys with no switch - try turning the volume down!!! Good luck and post if it worked!!

