My Exeo (B7 chassis) does the same, although with 'good' >6mm thread on the tyres. It's done it from new with Pirelli Pzero Rosso's.
I spotted the thread last year on here, with regards people saying it was tread depth, but mine was basically new at that point. I've got used to it now, and it appears to be down to the angle of the CV joint, and the angle of the wheels in contact with the ground when on full locl.
I've also got a 'grinding' noise when on full RH lock, which the Seat dealer can't fault-find. It's logged with Seat, so hopefuly they will come up with an answer..... maybe!