Hello Mr Lightpainter sir, now, your car is 2004 KV6 and it will probably have a two speed fan and resistor fitted.
I am assuming in this weather you have the air con on.
Usually your fan will come on at a slow constant speed that you may not hear.
If the resistor fails for the slow speed, the fast speed comes on and sounds like a hovercraft, stays on for a few seconds then switches off. Then it repeats the cycle continuously. You can confirm that yours is a two speed fan by looking through the radiator grill. Just behind the fan, at about the 2 o'clock position you will see a silver resister around 1/2 inch thick and 2 to 3 inches long, this is the culprit.
Under Ã‚Â£15 to buy from Jules is the upgraded gold version. Trouble is it is usually a bumper off job to fit it unless it is a mk1 75, then it can be done by just removing the grill. If you were closer I could have done it for you.
Hope that helps.