Recently had front brake discs and pads replaced. Within a few months, vibration and grinding noise appeared. Took car back to garage who diagnosed warped discs and replaced under warranty. A few months later, same problem and same solution, but garage unable to say what was causing problem. The grinding noise has now started again - can anyone offer suggestion as to what it might be/cause etc. Apparently garage has checked hub, calipers etc and all OK. Noise only happend under braking. Car recently passed MOT in between outbreaks of grinding !