I had this in my RR Evoque. It turned out to be a leaking gasket. On the Evoque it was quite a job to fix the gasket, had to remove some other stuff to get to it and the local Land Rover dealer quoted me over $3,000 to fix the gasket. I contacted Land Rover (USA) and they agreed to cover the cost, my warranty expired 3 weeks earlier! Really grateful to the guys - and also why I ended up buying another Land Rover when the time came around this year! The gasket fix immediately stopped the smell.