tweetymp4 for the win.

I installed a camera at home one time just for the heck of it with a 100 ft run of CAT5. Two pairs took power to the camera. One pair brought the video back. The last pair brought audio. Despite the unshielded audio twisted pair traveling 100 feet snuggled up against a video signal, which has a BUZZ at 60 Hz, the audio channel was dead quiet as regards electronic noise.

What I used for connections were a stereo RCA cable cut in half and stripped back, wires twisted together and crimped inside these connectors:



In other words, paying no attention to noise AT ALL and using stupid low tech hardware, just being sure ground at one end connected to ground at the other end, it worked just fine. But yours might not, as tweetymp4 says.