My 4C, now just out of warranty, developed very annoying squeaking from front left suspension about 9 months ago. Local Alfa dealer not able to trace the problem, but I suspect they didn't try too hard.
Eventually spoke to the guys at Alfa Workshop in Royston who confirmed that they had the same problem with their car and a small number of customers' cars. The problem appears to be the compound of the bushes and was solved by replacing the lower wishbone. I've yet to get this done, but it looks like the only option!