2015 Mercedes Benz C63 AMG sedan + estate spied testing on the Nürburgring

In the week of 2225 July 2014 we spied four prototypes of the allnew MercedesBenz C 63 AMG W205 undergoing testing on the Nürburgring Nordschleife. There were both sedans and an Estate being tested on the track. What caught our attention though is that the prototypes sound different compared to eachother. Check for instance the sound of the prototypes starting with an A in the licenseplate, and the C63 Estate and sedan with BB at the beginning of the license plate. Completely different sound. Perhaps