Some people get quite reasonable economy out of the petrol D40 - I've seen someone quoting low teens. It's supposed to get mid-to-late teens. Compared to diesels - supposed to get 10.5, but some people have gotten under 10 - the petrol model is quite thirsty.
However, driven economically you should expect to get 500+km from a tank and you'll have a decent amount of power too.
Just don't expect to follow us oilers through the river!
As for that noise - it's really hard to diagnose the sound of the text, so I can only relay what we've been told about before - it's possibly the clutch and/or pressure plate - which is not cheap, but if you take it for a spin and ride the clutch a little you ought to feel it not engage as well as it ought to. It could just as easily be the clutch pedal - some people have reported that coming loose.
For what it's worth it'll have a warranty. If you like the vehicle and the only thing is a noise, tell them to get rid of the noise and you'll buy it. Don't buy it knowing that it has a noise - otherwise they could claim "they knew about it when purchased, so it's not a fault we need to fix under warranty" - whether that's right or wrong, they could argue about it until the warranty runs out.