Falcon gearbox clunking

My 2007 BF six-speed Falcon gearbox has already been replaced and there is still a clunking noise when changing gears. A Ford rep told me the noise is normal. I have test-driven a new Commodore six-speed and there was no noise. It seems to me Ford can't fix this problem. It's a great car to ride in, but the driveline is very noisy.