Exterior "rattle" During Slow Speed Acceleration

[drifter]

Since taking delivery, 03 ES300 has a constant rattle during the slightest acceleration from a stop. The only time it can't be heard is when the engine is cold and then only for the first minute or so. Noise sounds like a low grade spark knock. Most noticeable with windows down, no traffic noise, and driving next to a wall or a crash railing next to the road. Test drove another loaner same model year and same noise occurred under same conditions. Dealer and regional rep say it's normal and won't do anything to determine what's causing it or attempt to fix it.

Ideas anyone?

[SW03ES]

A rattle? I dont think mine does that...

Can you describe the noise better?

[steviej]

nor my 02.

look underneath and see if a heat shield is loose. If it is an ignition knock, try a higher grade of gas and see if it goes away.

steviej

[SW03ES]

It could also be a loose clamp somewhere in the exhaust system...

[drifter]

Thanks for the replies. Don't think I can describe it any better. After I requested that the dealer at least put the car on the rack and look underneath and check for loose things they finally agreed. 4 techies walked around underneath, had engine running and in drive, couldn't reproduce noise on the rack. Back on the ground with car accelerating from stop noise still there. We checked all the heat shields and clamps, they weren't loose. Using high test or regular makes no difference. The true spark knock is very audible when putting pedal to floor using regular gas but the anti-knock sensor activates very quickly to get rid of it. The noise I'm describing is audible even after the anti-knock sensor has done its job.

More suggestions?