I'm not entirely sure I'd agree with Eddie's waxing lyrical comments about the sweet petrol engine in the 520i!

If I'm not mistaken, that engine is a B48, same as the ICE part of my 530e. At speed and on cruise control, the engine note is well subdued and things are quite refined, especially because the long gearing keeps rev's low while cruising (2k RPM at 120k/hr), but if you even mildly tickle the rev range above about 2750 it is not an overly refined, nor sporty sounding, engine. Not sure what it sounds like from the outside, but inside is a bit coarse. I may be spoiled by a lot of years and miles in straight 6 cars, but even after 3.5 years the engine note still makes me regularly do nostalgic searching for straight 6's on the various car advertising platforms.