That's a reasonable explanation, although you'd think Fiat would have got the right spec. oil for it by now (they've been making this engine long enough!) to stop it from tapping, if indeed that's what it is..
Mines the Selina 5w40 (i presume, as Fiat serviced it last, before i bought it.) It is due a service soon, and i'm sure that doesn't help, but it has been doing it since i had it, 7 months and 15,000 miles ago.
It is a bit hit and miss though, this morning when cold it was tapping, then as soon as it was up-to-temp, it was fine. The other day however, it continued tapping all day (quieter when warm). Very odd.