In the last 3 days, I've had 3 different instances of putting my car in reverse having it start to back up for about 1-2 feet and then completely lock up (feels like the rear axle/transmission area). The car becomes completely immobile with my foot off the brake. The first time it happened, I added a slight accelerator press to see what would happen, and the car acted as if it were in park.

In each instance, I have put the car back in park and turned it off for a short period of time before restarting it. The first time this problem happened, I attempted to reverse again and there was a loud mechanical pop somewhere in the rear undercarriage of the car but the car continued to reverse. Upon putting the car in drive and proceeding to move forward, there was another mechanical pop. For the second and third occurrences of this problem, I repeated the park/turn off/turn on/reverse the same way as the first time and there was no mechanical popping as I resumed reversing, but both times there was the loud mechanical pop when I put the car in drive and proceeded to move forward.