In the owner's manual under parktronic it should list a bunch of
factors that can cause the system to sporaticly freak.
These include weather like snow or rain, dirt or grime on sensors,
wax on sensors, RF or other things being transmitted from near by vehicles (radar jammers / radio equipment), cell towers, radio/tv towers, loud noises, underground wiring, metal plates or
man hole covers, excessive road heat or exhaust heat from cars,
ect...ect...ect.....just about anything that can mess up ultra-sonic
signals from the parktronic sensors.
It couldn't hurt to have the system checked for a faulty sensor
Best of luck.