I did this install with Keefe007, and was onsite earlier attempting to troubleshoot this.
I disconnected each cam one by one. The pic quality seemed much worse when there was only 4 cams live. It appeared there was a picture of one cam overlaid onto another cam - but it was oddly sliding from left to right vs the usual horizontal lines scrolling up.
I then plugged in another spare cam, but instead of powering it into the main power supply, I used a power adapter. Pic is grainer than I think it should be, but it is only slightly grainy. Definately no horizontal lines or artifacts that I can notice.
So I am guessing that there is some form of noise/interference that is coming into the system via the power box. Either the box is defective, or more probably there is a bad crimp somewhere in the camera network.
Going to check out the signal using an external monitor. Will keep you posted.
-WC-