another problem

Right I have a 1998 300tdi, when I put my brakes on I can hear a clicking noise from what sounds like the calipers but I have looked at these and there not loose or any play in them. The click only happens once and if I take my foot off the brake and then back on the click happens again. and I can feel it through the brake pedal. I did wonder could the pad fitting kit with the spring be worn and its the pads rattling but once the pedals pushed down the pads would be solid against the disc's
Anyone with any ideas or need more info