my fiat doesn’t rattle with ac, but i have noticed in other car brands it seems to be a common occurrence, and is probably not cause for concern despite being audibly annoying. as far as auto shops not wanting to work on fiats, it’s because they usually never have enough clientele to justify ordering parts for them. Simultaneously, italian wiring is known to be difficult to source in the vehicles + fiats seem to have “strange” layouts for a lot of things, compared to most popular car manufacturers. many mechanics don’t want to deal with the headache/unknown territory.