Fix Mazda3/Mazda5 rear end rattling or clunking

this is a checklist of things to look for on a Mazda 3 or Mazda 5 when you hear a rear end clunking or rattling sound.
If your brake calipers are rattling over bumps, but not when brakes applied, it may be your aftermarket anti-rattle bracket. Replace it with OEM bracket, which may have more tension and hold it properly.