I've been searching the forum and so far cannot find a symptom described that's similar a strange engine noise I'm hearing on approx 1 out of 10 journey's I make. I have a 2005 A6 2.7TDI (which is great) and have recently noticed that occasionally I get a very loud engine noise which makes the car sound more like a noisy bus than the usual quiet diesel I'm used to. When the noise occurs it only happens in gears 2-6. In first gear there is no unusual noise. If the engine is switched off and left for a few minutes, then switched on again there is no unusual engine noise. It will then re-occur on some other journey. Annoyingly this is one of those problems that has to be demonstrated to the Audi dealer - I haven't managed to do this yet.

I'd be grateful for any clues.

Thanks.

an issue to be sorted im sure, could be sticking injector/fuel pump out of sink