Hi people need help with my reverse sensors I and getting constant tone one of sensors was done changed it they are all have crackling noise took paint of them still the same solid tone in reverse help it's a st Mondeo tdci

Sounds like they are faulty, presume that your car must still be under warranty says you bought it in 2016, I'd pop back to the dealer you bought it from and get them to look at it.  Could be a faulty sensor, dirt or something like that.  I used to have that problem in a few mondeos I drove for work, seem to remember the sensors themselves not being able to properly detect what was there hence the constant tone.

Hope you get it sorted.

You can test by unplugging one sensor at a time, this will lead you to eventually get the sensors working and you know which is faulty

I had this on my focus as above unplug one at atime.

turn ignition on but don't start car up put in reverse then go under bumper n unplug each one then put your hand over each one you will find out which one it is.