We purchased the car 3 months ago from Arnold Clark and within the first week it was back in the garage with a horrible clicking and popping sound from the brakes. 

They apparently stripped and cleaned the brakes but upon receiving the car back they gave it to us squealing whenever I applied the brakes and also the clicking and popping noise was still there. Tearing my hair out at the problem I decided to strip, clean and copper slip them as none had been applied to the shim guides and back of the pads. This sorted the squealing but that clicking and popping was still there. Upon losing all faith in Arnold Clark I decided to take a proper look at the pads and shims. Turns it the pads and shims were a cheap budget manufacture and upon further inspection they did not truly sit neat inside the carrier. 

So I went to Ford and got genuine pads and shims which were completely different from the cheap budget crap. That's them fit and no more noises! 

This is just some information getting passed on as I could not find anything on the issue I had. 

Hope this helps anyone with similar problems.

Also a vehicle which is still under the manufacturer warranty must be fit with manufacturers parts. Therefore Arnold Clark should have picked this up when the vehicle inspection was complete.

what's the mileage on it? sounds not old enough to have needed replacement pads in it's short life.