Mine does that. I back out of the garage, hit the brake and the pads shift to the rear of the caliper. I then go forward, hit the brake and I get a 2nd click as the pads shift the front of the caliper. This is slightly worse than I would expect because the pads have over 100k miles on them. New pads/clips/shims would make this much quieter.
My rear pads were actually rattling on bumps. I used some brake quiet to "glue" them to the caliper and make things less rattly.