Sounds like the backup sensor is detecting something. First time it happened to me was backing out of a parking space with bushes behind. Locked up with a horrible noise and scared the crap out of me. Thought I'd hit something for sure.
Same, mine picked up a small bush, and locked up.
OP, U got
buttons (switches) under radio, just
disable when backing up. ALSO, in U Connect, there is a sensor sensitivity setting, make sure set to Low. But them sensors are weird, and sometimes U just have to reach over, hit the button and turn them off, just how it is. Mine scream and yell at me all the time, sometimes, backing up in parking lot, makes me check mirrors twice before backing and/or just turn them off till going fwd, their is no rhyme or reason how they sometimes work.