Originally Posted by AutoX Z

My car does it but I can't hear it at all. However it drives my girlfriend up a wall and gives her headaches sometimes. She describes it as just a constant ringing, no change in pitch, no change in volume, just as long as the car is running it rings. For the people that can't hear it my guess is your car, and all the other Z's you've been in, make the same noise its just out of your hearing range. I was in a band through college and spent wayyy too much time standing directly in front of my amp.

There was another member on here that somehow traced it to a wiring bundle around the ECU in the passenger footwell. The dealer replaced the ECU and he said the ringing got quieter but didn't go away completely. Might be something to mention to your dealer.