Couple of questions from a new owner

[Chappers]

Hello all,

I've got a few questions now that I've had a good few weeks with the car.

1) What's rattling in the rear left quarter? Sounds metallic, took the wheel off, shook everything, put the wheel back on, bounced the suspension a bit, can't hear anything. Then when I go over small bumps like drain covers or divots int he road, a tiny rattle.

2) Do 18s fit over AP brakes? Are they the same size as OEM? Thinking of getting some track / winter wheels sorted.