I went through this, even had two techs, and the service writer drive the car, couldn't hear it or fix it. Then the service manager drove it and suggested hearing tests for his employees. Turned out to be a VERY slight twist on the tab that holds the sway bar brackets to the frame. Someone on this forum suggested it might be this, but I looked at it and couldn't see the problem. It sure fixed it, though.
(Oh man, this car is sooooo fast.)