Front parking sensors

[Steve68003]

I have a 2014 insignia with fitted front and rear parking assist. Last 24 hours the fronts are detecting something in front but there is nothing near me. When I drive over 5mph they switch off. It's intermittent but still does it about 90% of the time. It is set out in 3 sections,left,middle,right. It shows on middle only. I have noticed that my number plate sticks out about 5mm on 1 side so could it be picking this up?.
Cheap enough to by if faulty but how easy are they to take out.
Appreciate any help as this is winding me up.