The amount of threads on this is quite amusing. For some reason tho, in other sections of the forum, few people seem to accept it when someone says it's a quirk of Fiats. They just bang on about it needing to be fixed, so i've given up trying to say it's a quirk lately.
But yes, definately a quirk and whilst im sure some other makes have similar issues, i've never experienced it in anything other than a Fiat.
Both my Puntos (Mk1 and Mk2) and the Stilo all do it, as have numerous other Puntos and (iirc) a Seicento that i've driven.
Some dealers will probably say 'bring it in & we'll fix it' but in reality it won't get much better & theyll probably cause some trim to start rattling in the process, so just get used to it.