Depending on the camera at one time we stopped powering the audio because even at low volume there was still noise. If you look underneath the driver side dash panel (you have to pull the panel down and the box is above the steering column area)...there should be a "multiplexer" (little silver box). If you hook the "blue" reverse wire up to that box it will power the audio in reverse.
This is assuming its the same model of course...but worth a try.
PLEASE do not send questions via Private Message, my inbox fills up too quickly. Post questions in the forum as a new thread so that other users can benefit from the answers. Use Private Messages for sensitive information only (VIN, Contact info or things you do not want the public to see).