TD5 - strange noise from the front!

Just got back from a return trip to the Alps and amongst a couple of other problems I was worried about a loud low frequency 'warr warr' sounding noise from the front of the vehicle.

My thinking ranged from tyre noise (a new set of ATs), diff , propshaft or wheel bearing noise. Hadn't noticed it before as mostly do slow driving.

The car was serviced by a lndy specialist before we left and he noticed the noise, couldn't see anything wrong, but thought it might be the new tyres.

Any thoughts???

do you get this noise when you break or when you have power down