I have this same issue. last time I was at my mechanic, I said he would have to take the cover off of the column and drive it around to try and diagnose the source of the rattling/squeaking. I decided to give this a shot today, so I took off the cover, started to drive around and voila! no more noise! some of the extrusions that surround the perimeter of the cover were a bit bent and worn out (when you bend plastic and it turns white when it's stretched too far). I guess the only option would be to buy a new cover but being a part for an LS 400, I'd rather wait and see if there's anything that can be done before spending my entire earnings for the week