One of the most common repairs on the Land Rover Discovery 4 is replacing the front suspension arms. Often an MOT failure and will show up on an MOT failure sheet refer to the lower suspension bush but it is much easier to replace the complete arm that it is part of as it is very difficult to remove the worn bush and press in a new one perfectly straight. Once new arms have been fitted it is important to have your vehicle 4 wheel aligned otherwise you will find your Discovery 4 pulling to one side and uneven wear on the tyres shortening their life .
The symptom is a clonking/knocking sound from the front suspension, mostly noticeable at low speed, a quick test is to drive the vehicle forward and in reverse at slow speed applying the foot brake. If you hear a clonk as soon as the brakes are applied then it is very likely to be the lower suspension arm bushes.