If the radiator fan on the 4 is the same setup as my 3, you have what is called an electro-viscous fan clutch coupling.
Most fan clutch couplings are merely viscous which means that the fan feels the air temperature coming off the radiator and engages as required. Land Rover adds an additional complication - the viscous clutch is also controlled electrically - that is the viscous part of the clutch might wish to engage or let go, but the electrical part overrides the viscous.
As above, while it is common for the fan to engage and roar at startup for maybe a minute or so on a colder day, and I suppose when the engine is hot, while one hears it at startup, one does not normally hear the fan noise when driving.
In your case, something is wrong with I suppose the electric portion of the clutch and it will not let go. I suppose failing so the fan is engaged is preferable to the reverse.
For me, it was a new fan/clutch assembly - they are not free either.