Seat Leon surging and rumbling noises from fuel tank

My 12 weeks old 2014 Seat Leon has started making surging and rumbling noises coming from the fuel tank.

The noise is very loud both on the in and outside and occur at low speeds, accelerations, braking and reversing. It happens with a tank that is full to half full.

My local shop acknowledge that the sound is irregular but they have showed me a TPI from Seat which states that the problem is caused by the specific construction of the car and the dynamics of the fuel.

Since the sound is due to the construction they will not even try to fix it under the warranty. I just have to live with the fact that they have constructed it in such a way that it makes loud noises. They do not see it as a construction error.

So my question is. Have any of you, especially with diesel Leons, experienced any similar sounds from your fuel tank?