Doesn't sound normal to me. If the dealer won't drive the car at a speed that will provoke the noise why not try recording it and playing it back to them.
I got 42mpg @57mph on the m4 from Porthcawl to Swansea!!! Must off Been driving into the wind lol. It was mind numbingly boring though.
I was going Swansea to Porthcawl....
No wonder - it's downhill
Yeah that's the downside with importing. The price starts of competitively and then when the good arrive on the shores of good old Britain, the government take their slice and all of a sudden it's not such a good deal