I have this exact same problem on my 2010 Lexus HS 250h. When I bought the car (used) it did not make the noise. I drove down a 20 mile gravel road about 18 months ago and now my steering column rattles any time I drive on a rough road. A single bump isn't usually enough to cause it, just repeated bumps. I replaced the struts and had no luck. I have looked at the shaft under the dash and there is a little play in the u-joints but it doesn't seem to be enough to cause the noise I am hearing. A friend of mine who is a diesel mechanic thinks I need to replace the intermediate steering shaft because he thinks the u-joints are bad. I am not convinced. Any thoughts about this? I have never heard of anything like this, especially on a Lexus that is only 12 years old.