If it's the same whirring noise I had on my 2 litre, it's a wheel bearing.
Sounds nothing like any other wheel bearing I'd heard before and thought it might be something on the differential. Took it to the specialist independent I've used ever since and he diagnosed it immediately. (The 2 litre had been into the place I bought it from 3 times and they'd stripped down the rear right twice to try and find out what the problem was with no answers before I took it to the specialist)
Hope you get things sorted.