did you tried KojiH Homepage ? There´s a lot of infos, especially "Rattles and Squeeks".
Try this: Rattles & Squeaks". Then press "ENTER", choose "Repairs", and choose "Squeaks and Rattles". This should helps of any probs.
It's just that our cars are getting up in age and the plasitcs are beginning to weaken and bolts are beginning to come loose! Tighten as many bolts as possible on your dash and that should solve your problem...I think Aaron did this in his car and it solve his problem. Honestly this car's fit and finish quality is sooooooo much better than my TL's and that car rarely gets driven and it's 6 years younger!! The TL has all kinds of squeaks and rattles far more than my Legend...