When I put my foot down on my Audi A4 1.9TDI I see a load of smoke come out behind me. I have noticed this on other desiel Audi but never notice it on other desiel BMW. Is this a problem with Audi general? Is it a problem with the way the owner drive the car? Is it something to do with servicing or the engine? I find this very very embrasing? HELP!! Thanks