The radio communicates with some of the other modules over the CANbus network. After locking the car all of the modules should stop to communicate. If there is no communication the CANbus network should enter sleep mode after a certain time.
In your case the radio prevents the CANbus system from entering sleep mode. I have seen before that a defective radio still tries to communicate or puts a small voltage on the CANbus network which can be recognised as communication. This results in the fact that the CANbus system stays active which can drain the battery in a relative short time.
My experience is that replacing the radio solves the problem. Which type of radio do you have?