OK. Here is the scoop on this grinding noise at start-up. As I reported previously, my dealer finally diagnosed the noise in my IS350 and noted that a TSIB was issued to remedy the problem. Thanks to Member 'mehullica', I can report that the TSIB number is EG019-07, titled "Brief Enginer Knock/Noise at Cold Start". It is designated for IS350 '06 - '07's. It covers these model years for VIN #'s before JTHBE262#72009954 (TMK Producing Plant) and JTHBE262#75015099 (Tahara Producing Plant). The required repair is covered under the Lexus Powertrain Warranty (72 months or 70,000 miles).
As I read through the TSIB, I was astonished at how invasive the repair proceedure is. Virtually the entire top end of the engine must be dismantled including the intake cams (left an right). The repair involves replacing the intake Camshaft Gear Assembly and is estimated to take 6 hours. I certainly hope that the dealer service techs are well trained for this major repair.
Not exactly what I bargained for when deciding to purchase my first Lexus. I went the Lexus route versus BMW to avoid this type of major headache. Will be my last Lexus if my dealer can't make it right.
Anyways, hope this is helpful for those who have experienced this issue. I will report back with the results of my repair experience.
Hopefully the attachment of the TSIB comes through with this reply.
L_EG019_07.pdf