Constant clicking noise when engine is running

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The noise is constant and doesn't change with acceleration, idling, gears, breaking, etc. Starts when you start the car, and stops when you turn it off. We can still hear it when the stereo is on. Lexus svc said "don't worry about it", it is "normal", and related (somehow) to the fuel injectors. Web searches have not offered any explanations beyond similar claims. It is, nonetheless, annoying in its own right, and especially aggravating given the car is new. Any hope, explanations, or suggestions to offer? Thanks.