2001 Land Rover Discovery 2 Unusual Noise

DO YOU ONLY HEAR THE NOISE WITH THE FAN ON AND DOES THE NOISE CHANGE PITCH WITH THE FAN SPEED?

Yes, the noise is on only when the fan is on, and, yes, it changes pictch with the fan speed (much louder when the fan is on high speed).

With the information you have provided I would have to say that there are to possible causes. One, the is debris in the fan, Two, the fan motor is bad. The fan can be accessed from the passenger side of the dash. Remove the cardboard under dash panel (3 clips), unplug the motor, and remove the 3 screws holding the blower motor in, carefully lower the blower motor. At this point you can clean the debris from the fan, if there is no debris then it is likely that the bearings in the blower motor have failed.

If the bearings in the blower motor have failed, what needs to be replaced? The blower motor or a whole system?
Thanks you in advance for your response

If the problem is internal bearing failure, then you need to replace the blower motor itself. Depending on where the part comes from it may or may not include the fan, but it is easier to get the blower motor assembly, which will have the fan already mounted on the motor.