I have just been through the same thing. After replacing the uni joint (as mentioned in the previous post) in the steering column the rattle was still there. I got to the bottom of it last weekend when I adjusted the pre load on the steering rack. The correct way according to the workshop manual is to measure the resistance on the steering pinion with a 0-5Nm torque wrench, but who has one of those? I just tightened the 24mm hex bolt until I felt very slight resistance when moving the rack back and forth. I used an old 24 mm bolt as an adjustment tool. You will need to pull the rack out to do it though. Took about an hour or so to do and the rattle is gone. Careful you don't go too heavy on the pre load as your steering will not return to centre properly. I suspect all the money I spent replacing bushes, bearings and ball joints on the front end was unnecessary but at least I know it is all sorted now.