You generally won't hear them unless you are sat in traffic in the height of summer with the AC set on LO.
There are a few trigger points for the fans for just engine cooling (AC off). Stage 1 is usually around 95 degrees at a slow speed, stage 2 is around 105 and full pelt is usually around 120. It's very rare you will hear them running fast enough to hear them in the car, except for my first sentence
As I say, if you have VCDS or OBD11, do an output test on the fans to confirm they are loving life and got your engine's back
