Sporadic whining noise Mondeo ST220

[cortinamarque3]

Hi
I am starting to get a really sporadic very loud whining/droning noise from the front of the car when driving at medium to low speeds. Happens when pulling off but also when in motion. It is very loud but no warning lights come on. Can't be brakes as the car is in motion when it happens- it lasts from 1 to 3 seconds. It is quite a high mileage car 150000 miles.
What on earth is that do you think?

Thanks Matt