feedback issue on dvr sound

I have just installed a supavu dvr (http://jsrcctv.co.uk/images/D1%20DVR%20Manual.pdf)

concept pro ptz dome, microphone on a job and I am getting feedback of the audio.

I have cabled everything back to dvr, microphone wired into audio in ch1, and a cat5 cable from audio out which goes to another room and is connected to a projector. I have also taken a video signal from the same cat5 cable.

I tried wiring into mic in 3.5mm on projector, it stays normal for a second, and then the feedback starts, also tried wiring it into the rca audio in, but it is very quiet, with a very slight amount of feedback.

would prefer to get the job completed fully when I return, so any suggestions welcome

What I did notice though is the 3.5mm jack plug I was using had 2 wires and ground, (for left and right audio channels?) could this be causing the issue?

thanks