Ok, the slight bump sound tells us that the Electronic Selector Module (gearshift) is getting the signal from the brake pedal to release. The release mechanism in the module most likely has failed. You will need to have the module replaced and initialized with a Mercedes diagnostic scanner in order for it to work. In order to get it out of park I've had success starting the car, applying the brake and grasping the shifter with two hands and shaking it vigorously while pulling backwards. You can also remove the shift knob and rap the top of the shifter firmly with a rubber mallet while pulling backwards. Let me know if you have any questions.