Happened probably the same day i got it cleaned as I was reversing what looks to be the near side i'm a good distance away from the wall, it bleeps as if there is something behind the car but I know for sure there isn;t (for a good few foot at least).  What I find strange is, it's okay once it's been raining or first thing in the (cold) mornings.

 

Im baffled.

The exhaust gas makes mine go off which could be the cause of yours as well.

Repost deleted.

Edited 3 March, 201610 yr by pkr

Nope never had it before.

make sure you've cleaned the sensors well, and make sure you haven't left any wax/ polish on them