The thermal switch for the fan is on the thermostat block (under the tank at the front rhs), but your fan sounds fine... they usually only come on if it's a hot day and you've had the engine running for 10 minutes without moving.
(Last time I changed the radiator I left the fan off completely... it gets in the way when refitting the rad and is never called upon to run, on the rare occasions I do have to wait in traffic for a long period in hot weather I turn off the engine anyway.)