When I first had my hatch I felt the brakes were wooden in comparison to a lot of cars I had driven, I checked all the pistons were free flushed the fluid through with fresh 5.1, they were great at stopping the car but were just different in feel - there was a lot of additional pipework for the antilock and traction control that I had not seen before in a braking system so in the end I put it down to being the modern disconnection with the brakes themselves.
did the dealer have an opinion wrt the cold rattle?