had the car in to audi main dealer for cambelt change last monday, when i took it home the traction control light came on. i brought it back and they said the injection pump timing was out so they sorted that. car seemed really good, very smooth and quiet and loads of power. then on saturday accelerating at about 20mph i heard a horrible noise, like a crunching. i swithched off the engine, pulled over, and had it lifted to the same main dealer as before. they have it two days now and still no diagnosis. they said they started her up and she purred, please help