Taken me a bit longer than expected to get the car into the garage, but as promised, a bit of an update on this issue.
Car has been inspected by garage and a Fiat tech. Apparantly the noise is coming from the ABS module at low road speeds.
According to them this is perfectly normal.
I'm suspicious myself as I havent heard it on other models, in fact the courtesy car we had (admittedly a 2010 model) didn't have this noise. So would be interested if anyone else has heard something similar.
Suffice to say it's been reported whilst under warranty and we'll see if anything develops further with it.
As with a lot of high pitched noises, maybe some people's hearing is more sensitive to it, but both me and my girlfriend can here it very clearly.
Gary