I'm suffering the same problem along with squeaky brakes and a groaning clutch pedal.
My 159 is less than 2 years old has 21k miles.
It is in at Dews Alfa, Brighouse, W.Yorks, who aren't covering themselves in glory.
3rd time it as been to them for the squeaks.
They seem to be employing see no evil, hear no evil...speak lots of evil!
Last visit I took a mechanic out with me and wouldn't take him back until he acknowledged the cacophony wasn't just my imagination.
Having been serviced by them within the last 2 weeks and the brakes being declared ok for wear and damage etc, they phoned me today to tell me they wanted £130 to strip, clean and re-fit the brakes, When I asked about the other noises, they said they couldn't hear them, so couldn't diagnose them!
I've complained to Alfa Uk customer service. (not sure I'm that optomistic they'll resolve to my satisfaction).
What is anoying is that the squeaks and groans and possible solutions are here for all to read, so why doesn't an
Alfa dealer know anything about them!
Expecting an update tomorrow, meanwhile I am holding their courtesy car hostage.