I've noticed that my front brake pads rattle in their calipers. I notice it especially if I brake after changing direction at slow speeds ie. reverse out of my garage. I've checked and everything seems to be assembled correctly, pin, retaining clip etc.
The pads are brand new Brembos. I changed them about a month ago, and maybe they have 1000km on them at most. I seem to remember the old ones doing the same.