It's a like an old WW2 Bomber drone.Sort of a dull Wah Wah Wah sound.I initialy suspected tyre noise as i run a fairly aggresive off road pattern tyre (I have a house in darkest Shropshire UK) and do have to tackle farm tracks,flooding and generally bad road conditions.But it's not the tyres.The main givaway is driving around a corner at around 30MPH/50 odd KPH.You can hear the note change as you load/unload the bearings.It's only my left front,but am replacing both.

There is no movement at the wheel (Top/Bottom) on a ramp,and suprisingly very very little noise whilst spinning the wheel.Apparently mine is only in the early stages.