I've got a problem with the NSF caliper on my wife's Zafira B CDTI.
The caliper has just started grinding against the inside of the alloy wheel. Nothing has changed on the front brakes/wheels for about a year when the pads & discs were last replaced.

I've taken the wheel off & there's nothing loose or caught between the caliper & the wheel. It just looks like the sliding section of the caliper is pushing outwards as well as clamping the disc. The grinding happens irrespective of whether the brakes are applied or not.

The wheels aren't the ones that came with the car - they're a 16 inch astra coupe alloy but they've been on the car for at least 2 years now & although they are snug, they haven't come into contact before unless the wheel weights are put in the wrong place.

Does anyone have any ideas what this could be? Is it a common problem?