Brief startup noise only when cold
I seem to be having a very similar problem with my 159 Ti 2.4JTDM. For me, as soon as the outside temperature gets below about 4 degrees (definitely does not have to be freezing) and the car is left for many hours (typically overnight) then on first start up in the morning I get a rasping rattle which comes and goes for anywhere between a few seconds and a few tens of seconds - the duration of this noise seems to depend upon how much below 4 degrees you are. When I lifted the bonnet and tried to find out where the noise was coming from it was hard to be very specific but was probably loudest in an area around the alternator and water pump. Does this also fit your original description? Where is the steering pump? It would be great if this is likely the same thing as last time I mentioned this issue to the dealer, they had no idea what it was because the weather wasn't cold enough to make it happen.
Unfortunately I also have another noise that seems to last a bit longer... again only being clearly noticeable on a cold day and lasts for a few minutes this time. This one is more of a wining noise like a rubbing belt sound and again, under the bonnet, there is a very loud ticking noise from an area around the water pump. Perhaps this is something completely different.
Anyone got thoughts on either?