If it whines only in gear then it is drive train related.
Either any of the following:
: jack up the front of the car and place axle stands under to make sure it secure
Leave the the car in neutral and slowly spin each front wheel, if you hear a low grumble then spin the wheel faster. If it gets louder or higher pitched then the wheel bearing needs replacing usually as a complete bearing assembly and not difficult or pricey in comparison to other marques.
: Tell tale signs are splits in the CV rubber boot where grease has escaped leaving it dry While the car is still up on the axle stands turn the steering wheel on full lock both ways while rotating the road wheel, if a constant grumble and slight clicking occurs then it will be a CV joint.
: See if the noise is coming from furher along from the shaft it could either be inner joint or a bent shaft itself so get underneath, mark with a pen a point on the chassis you can see behind the driveshaft and watch it while a helper is rotating the wheel. Does the mark disappear and reappear i.e. hopping? Then the driveshaft is bent. A common problem on 2.4JTD's in particular, due to excessive torque on changing down and giving it welly!!!! Ask my brother in law, he knows how to chew them up good and proper!!!!
It could also be alternatively brake disc
related too... Do you have a lot of corrosion on the centre rim and leading edge of the discs? The rust can make the pads hop and catch at regular intervals creating a whine or grumble at lower speeds.
Hope this helps you locate the problem mate