Freak rattling noise still a mystery
Sorry, I can't bring any answers, I shall just give you my story.
I found your post trying to get an explanation for my problem, which might be the same as yours.
My car is a 2002 147 JTD. That noise first appeared end of 2004, after no prior incident of any kind, and it would then occur when starting the car every time the temperature would drop to zero (Celsius) or below. I was a continuous rattling noise apparently coming from a spot somewhere behind the front panel on the right side, in the engine compartment or near the right front wheel. The noise could be heard more from inside the car than from the outside.
For years, I mentioned it to my Alfa Romeo maintenance service, but since the noise would stop after a few minutes (never more than five), I was never able to make a mechanic actually hear it. I was told that everything had been checked and re-checked and was OK, that nobody else had ever mentioned the same problem, etc. etc.
For almost eight years, the noise would come back sometimes in winter, always following the same scenario, but not systematically.
These last two years, though, the problem has become worse : the noise does not last longer, but starts unexpectedly, without any link with low temperatures, even when the car has been running for a while, most of the time after going over a slight bump or dent of the road surface. And it can happen repeatedly in a single trip... With a bit of luck (?), in the meantime I was able to make a mechanic hear it, and listen to it carefully. Everything was checked again, and the result was: there is indeed a strange rattle, but we have no explanation for it; the car is in perfect condition.
After almost 12 years and 180 000 km, I consider my car as very reliable on the whole, and that noise it still my main issue of discontent to this day. But I find the situation very un pleasant.
Should a solution or even a hint come up on your side, I would be grateful if you could let me share it.
Sorry for my stilted english.