Also a loose pad can cause both a rattle and/or a squeal. The rattle would normallty disappear when brakes are applied if it is brake related.
If they are GM calipers, the outer pad should be cinced to the caliper by its ears, and should not move. The inner pad clips to the piston to hold it. Some type of anti-squeal (shim and/or lubricant or adhesive) can be used on pad backings where they contact the caliper/piston to absorb some high pitch noises as well.
Some pads just like to squeal, and are just inferior. The clunk is what you really need to find before driving again.