Parking sensors

Hello,

this is my first time posting so please excuse if I don't get it right. I have a 13 plate Citigo with original parking sensors. They usually work but recently when putting the car in reverse rather than the usually confirmatory bleep that all is ok I get a loud clicking sound out of the speaker. After a few clicks sometimes the confirmation bleep sounds and it works or the bleep does not come and the sensors do not work. Is there any relationship between the amount of clicks and the possible fault like flashing out a code on old cars or is that just random? Any suggestions where to start looking or how to find the fault?

Thanks

Christoph