Just because they're clicking doesn't mean they're working
They can be clicking but not picking up properly causing the parking sensor ECU to give the dreaded continuous beep.
On T4 it's easy to see which one isn't working on live data by walking past each sensor at the same distance and noting the readings. Sometimes it's more than one
Without T4 the only option is to get hold of a couple of new or known working sensors and fix it by a process of elimination.
Russ