Vibration on the floor while turning

Hi...This is my first time on this site. I have a 2002 Grand Prix GT. I bought this car certified used, but since the day I bought--I am feel some kind of vibration on the driver side floor bed when I start the car and turn it- right or left. this vibration does not come during normal driving..and only when I initially start the car and drive.
The dealer did replace the Rack and pinion--but still i am getting the same thing--and the dealer is not able to figure it out..said its normal.

Can someone help me with this.....since my car is under warranty, i can get this fixed if I know what is wrong with it.

Thanks

I don't know what it is but it is not normal. Might be a wheel hub starting to go bad.