[driver01]

The E-brake is a drum style of brake, while the service brakes are disc brakes. Both the E-brake and service brakes are housed in the rear using the same rotor. The raised center portion of the rear disc holds the E-brake which is mechanically activated, designed to work even if you get a hydraulic failure with the service brakes.
The clunking noise is from the shoes locking up against the drum. They kind of wedge against the drum once applied creating the clunk noise.
On the first picture you can see the larger center section of the rear
rotor that houses the parking brake components.
The second picture is an exploded view of all the parking brake components.
The shoes have brake material on them, once this wears out you will get
metal to metal contact and ruin the rotors. In order to check the shoes the rear rotor has to be removed, I do not believe this check is part of regular service.