I have an issue with my rear parking sensors no longer working. What happens is when the parking sensors come on I get a constant high pitched noise as the car thinks there is something right behind it, an orange triangle with ! inside it shown on centre screen behind car. The front parking sensors work fine but the back ones have this issue and no longer work. I have looked at the parking sensors and they all look perfectly normal. I drive a 2014 Fr and was wondering if anyone has had a similar issue and how can I fix it?