FYI: Alfa 159 v6 Q4 metallic rattle at 1500rpm
My Bella had recently developed a resonating metallic rattle that sounded like it was coming from the RHS of the engine bay. It would appear most noticably during fast idle when she was cold and decelerating throuh the Rev range of 1500 to 1300 rpm.
After a bit of exploration underneath I found that the bracket holding the exhaust coming from the rear bank (closest to the firewall) onto the transfer case had sheered off. Hitting the exhaust makes the flexi-joint shake like a maraca.
Running the car is much worse!
Heading to the exhaust shop tomorrow to have things welded back up and re-enforced!
Thankfully it wasn't something more expensive and you can see it without having to remove the splash shield.
Hope this helps someone else with this problem!