Play in steering and knocking

When the car is stationary i can move the steering wheel a couple of inches on either direction and get a small knock noise which sounds like its coming from the middle of the car. But when im driving the play is gone and there is no knocking same if i jack the car up and get someone to move the steering i cant see or hear any play atall. Im thinking its the track rod ends going but im told the track rods themselfs are most likely the problem. Would anyone agree with this and how hard are the track rods to change. The cars done 120k now and ive never changed a bush yet so im planning on changing wishbones front arb bushes and would do the rods at the same time.