I have the same problem you have with the "rattling" or "grinding noise" at start. On March 8, 07 I took my car to Lexus dealer, they checked and they replaced the driver's side sprokets. Then the noise goes away. The car runs great for about a month. And now the noise is back again. It really frustates me. I called the Lexus dealer again for the problem. They have scheduled for my next service on May 31. One of their technicians told me that the Lexus engineer did know about this problem. They are working on it and hopefully they will soon redesign the new cam sprokets. If you know any information about this problem, please let me know, I'll appreacite. And after I have the service done with my car this time, I will let u know too. Hopefull they will solve this problem for us.