Hi, me again with my questions. What makes the older diesels less refined and noisier? Take the 2.5TDI Tiptronic, at pulling away speeds it sounds quite loud. I've read things like 200ml of 2 stroke cures this as new diesel doesn't have the same lubrication as older diesel due to regulations, etc. But what part of the engine is actually making the noise and are there any other things that can be done to make it sound smoother?