So, there's nothing wrong, huh?
A friend at work happens to have exactly the same car as me (159 1.9 LE Saloon), delivered 5 days after mine (December 08). I have just been out with him for a test drive in both cars.
Conclusion : the noise is definitely a problem!
His car does not make the noise at all. In addition, his car's steering is better, the gear change/clutch is better, and in particular, the engine feels MUCH better (acceleration is significantly better, much smoother, quieter, etc.). He said after 1 minute driving mine: "You've got a serious problem here, mate! I'd give Alfa hell." So, it's not just my imagination....
It's already booked in at Dew's on 14th, with the Alfa guy coming to have a look as well. I'm going to make it very clear this absolutely their last chance to sort this car out before I demand a replacement.
Update to follow!