Cheers. It's on standard 17" teledials and 225/45 P Zero Rossos, all fairly new. I can's see any rubbing damage on the tyres or wheels, inside or out.
The noise is a very high-pitched, and very metallic, sound. I think the engine undertray is in good nick, I'll have a better look around it. The rear wheels used to rub in the arches on my last 156 when driving hard with someone in the back, that was a very different sound.
More pressingly (and annoyingly
) I clipped the rear wheel arch on the entrance to the tunnel to my parking space today so will be making an appointment with Chips Away very shortly - while it's in my garage I might jack it up and have a look around the underside...