If you lost a clip from the hardware this could most likely be the cause of the noise you hear, because now there is a gap between the brake pad and the holder it rests in. If you buy a set of caliper hardware you can easily fix the problem. Also did you double check your work and make sure eveything was tight too?
The best way to stop the rear brakes on a Mazda 626 from rattling would be to replace them. New brakes can cost between $20 and upwards of $100 depending on the quality of the brakes.
Even though the brakes were recently changed, I would have the brakes taken apart and inspected. Something may have gone wrong.
Check the other side for comparison
it depends on where you go
I need a daigram of the rear brakes being changed
you go to a mechanic and change*
the brakes
due to bad cordination between gear and cluch causes this effect
I would have the brakes checked ASAP. As to the rattle there maybe a nut that came off something and is inside something and the bump makes it move. The two may not be related.
Check the 1994 GMC Safari's brakes. Even if the brakes are fine, dust can cause the components to create loud squeaks, rattles, and sometimes ringing noises.
If you suspect something, get them checked. If you get vibration while applying the brakes, get them checked. If you get grinding noise from the brakes, get them checked.
The grinding could be coming from the rear brakes.