Dealer service rep tells me a thumping sound from under the hood that occurs with 20 feet after starting the car is inherent to the power steering apparatus. He claims there is no danger, but what an irritating sound. He also said it's found in a number of G35s, that Inifiniti is aware of the noise problem, but won't replace the motor because it's not considered dangerous. He said its just the coldness of the car pushing the fluid. Has anyone else experienced that noise?