If two different mechanics, including a fiat dealer, already put their hands on your car, there is not much that I can say.
This kind of noise are often caused by bad rotor discs or locking up brake pads, I assume that this had been previously checked and fixed .
about the steering rack problem, when the steering rack has troubles the noise is from the steering rack itself and from the front of the car, if you are sure the noise is from wheel check brakes, or, if the noise does not cohincide with braking, check the wheel bearings.
See here on common brake noises, cause and identifying them.about "fiat would not allow any more work on this problem", that sounds a bit like rubbish, call Fiat in your country (put Fiat in google, then find support/ contact), and ask them about their policies. I do not think from description this has got to do with steering, unless you get the noise only when steering, nyou usually get also vibrations on steering wheel in this case.
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Many thanks
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