slovin

Can anyone help 05 plate freelander had front tyres close to illegal, so replaced it seems however that since replacing front two tyres the car has developed a droning noice, no vibration and no wobble just a noise that seems to come in at around 45mph that makes you want to pop your ears. I have heard that due to perminant 4 wheel drive you should replace all 4 tyres at the same time is this correct??? i put a tread depth gauge on all 4 and the rear two have approx 3mm less tread depth giving a diameter difference of about 6mm, does anyone know if the rolling radious offset is likely to be the cause as it is too easy to convinse myself rather than being objective and at the cost of the tyres it would be good to have some degree of certainty. Many thanks in antisipation.
Steve.

Problem with traction control on 05 plate freelander!
could any one point me in the right direction please, periodically my traction control and yellow hill decent light come on when braking, this happens at low speed braking and TC not actually operating, sometimes as i let go of the brake pedal the lights go off and sometimes they stay on until i press and release the brakes the next time, this however happens on some days and not others, i have a feeling it is a faulty sensor somewhere as there are no other symtoms and it happens too randomly.
Any guidence on the matter would be gratefully appreciated.