What is contained in the large black box hanging in the trunk of your 1999 Olds Aurora?
Not sure if it is the same as mine but could it be the CD changer? Mine is black and is mounted on the right side of the trunk. Found the answer at an Olds dealer and it is a factory installed Sub-Whoofer Stereo System, which cannot be removed. Answer Bose subwoofer. Remove rear seat. Remove rear deck. Remove screws and lift out subwoofer enclosure. I took a Dremel tool and cut off the enclosure. Also cut out the top and anything keeping me from attaching a piece of plexiglass. I then bolted the plexi in place. Then cut new holes for new component speakers. Reinstalled reverse of removal. Then added enclosure and subs and amps that I prefered.