mike1

You have described this problem very well. My 350 developed this at around 5000 miles also. It now has 12,000. Dealer has been unable to diagnose due to being very intermittent. Recently took car in for annual safety and emmission inspection and told them to keep it until they diagnosed noise. To my surprise (one day later), dealer called and said they found the cause and it is described in a Technical Service Bulletin (don't know which yet) and that parts were ordered and will be repaired under warranty. I was told it was something to do with one of the overhead cams (chain tensioner possibly??). Any ways, for those that experience this annoying noise, sounds like there is a solution. When I find the TSB number, I will pass along. Thank you. I appreciate any update on the TSB. I now have 13000 miles and the noise never stopped. In fact I think it got worse in the sense that it makes an appearance every time I start the car, and not just every once in a while like before. My 15000 mile service is comming up soon and I'd love to get rid of this noise once and for all.

** UPDATE ** I realized that there is a link between the gas I put, (not the octane, which is always 91 or higher, but rather the gas station and the quality of gas you get there) and the noise at start-up. In retrospect, I noticed that the noise made an appearance when I filled gas a couple of times at gas stations other than the one I usually go to. I am very particular about putting at least 91 octane, but it is more than likely that the gas was not up to standards at those gas stations. Maybe your neighborhood/usual gas station is not consistent with the quality of gas they sell you. The noise may well be a side effect of impurities in the gas. My usual gas station is Chevron which is near my house and I've never had a noise problem when I filled gas there (I always put 93 octane). Since I filled about two tanks of clean gas there, the noise completely disappeared, and for the last few weeks NO NOISE! From now on, I'll make it a point to fill gas at my usual gas station and keep close attention if the noise makes another appearance. Good Luck!

I have the same exact problem, just as I start the car and the engine crancks, I hear a brief metallic rattling noise, it actually sounds almost like the noise you hear when you stick a paper in a fan for like a second (except more metallic). It is really frustrating because it doesn't happen every time so it's hard to detect the cause/source. I have my IS350 for about six months and it started a couple of weeks ago just when I crossed the 4000 miles. When I took my car in for the 5000 miles service a few days ago, I reported the problem to the Lexus service dept. When I got my car back I was told they checked all possible reasons, but since they were unable to duplicate the noise they couldn't make a detrmination of what's wrong with it and as far as they are concerned the car is OK. Will keep trying to figure it out and inform you. If anyone manages to solve this mystery please let me know. Thanks.