Sorry, I can't help you, but I had the same problem myself when fitting a Saris Bones 3. It was mainly due to one of the wheels hanging down too low. The bike doesn't have a straight cross bar so it hangs at an angle. I searched in the menu settings for some PDC options but nothing.
I would have thought with a rear hitch system like yours that when all the cabling for the light board is connected that it would disable the rear parking sensor. I guess I will have to just live with the sensor going off when in reverse and wait for the crumpling sound of bikes
