I've been getting some "heat shield like" sounding rattle from the under side of the car when taking off. It seems to be coming from under the engine area, I don't think it's the heat shield over the cat sine I've had that before and that was the first thing I checked, it's all tight.

Is there another shield under the engine that can cause this? It's embarrassing

 

Hard to say what issue you have, but I have a non Lexus car which developed quite annoying rattle noise only happen at 800-1000 rpm while taking off for about 6 months, the rattle noise seems coming from behind wheel or somewhere just right bottom of engine, check the heat shield and all possible loose bolts or screws or loosing parts behind wheel and underneath of engine in vain. it is definitely a loosing parts rattle I am pretty sure but just can't find it!

I finally got the problem solved by lucky while I change oil and oil filter under the car, I touch the transmission protection cover just behind oil pan and found one cover corner has a bit loose, I tighten up that screw without thought, after works done I jump into the car for a test drive and surprise finding that rattle noise has gone!

BTW, I have ramp which I can safely go underneath the car to check.


Good luck!

 

It might be from a black plastic trim directly underneath your driver seat under the car that is no longer attached to the metal. What I did was get heavy duty double sided sticky tape, cleaned the metal and plastic real well with soapy water, and stuck it back. Theres a thread on this 2nd gen rx board about it, but too lazy to search for it right now.

 

Had the same issue with my wife's RX350 and it was the brake line plastic shield right under the drivers side mid way under the car. Instead of taping it back I just trimmed some of it off because I am sure if taped back it will fail again due to the weather it is exposed to.