2014 Ghibli diesel -I recently suffered a flat battery overnight,cause still unknown,car has been fine since after resetting all fault codes except when pressing sport mode the exhaust note no longer changes , could a fault with the system be the cause of the flat battery? coincidental? any suggestions on the reason for loss of exhaust note? Im in Liverpool and a lot of garages wont even look at the car and theres little resource in my area so any help would be gratefully appreciated,thanks