hi guys & girls , i got a 2004 audi a3 2.0 TDI , semi auto tip 58.000 miles diesl , when i at the lights with the car in drive it makes a crackling/popping noise l, when i take it out of drive in to neutral it stops , but it doesnt make a noise when driving and still pulls and drives well , please could some audi wizard tell me what it is , are what id be looking at to fix , thanks very much for your time and help ......dave