Just an update on this. Took it to the local Alfa specialist yesterday and he confirmed it is the alternator bearing. He has one he's taking off a 156 with 40k miles on it that I can have for not a lot of cash so that's a result. Then on the way back I noticed a horrible loud chinking or ticking noise, only under load at about 2500-3500 revs. I initially suspected big end bearing but I can't replicate the noise in neutral, I also haven't heard it again since despite driving it up a couple of hills. I now suspect it may be the auxiliary belt chirping because of the alternator pulley being out of whack. Will investigate further.
Last edited by Simon_GT; 06-09-15 at 09:53.