Yeah,
I have 2010 RX250 about 20K miles now. Yes, I heard it too, but it will be gone after 5min.
I took it to lexus dealer and they said it just normal. When the car get cool start, the fuel Injector will work with max speed, that is why you hear the noise, but when the engine get warmer or warm start, the fuel injector will work in normal speed, so you will not heard the noise.
Even the noise does not hurt the engine, but it hurt the owner alot. When you spent more money to buy expensive car like Lexus, you don't expected to heard some noise that the cheaper car don't have it.
That is what I told the service manager.