I bought a 2007 Audi A4 TDI ten months ago with 25,000 on the clock and a 12-month Audi warranty. When setting off in first gear it intermittently judders, particularly when the engine is cold and on hill starts, no matter how carefully I set off. The Audi garage claims not to have noticed it when I have taken it in for checking. There is now only one month left on the guarantee and I am worried it could be something serious and that Audi will refuse to accept responsibility once the warranty expires.