Omaha/Bellevue pixelization

I am having pixelization on channels 5, 8, and several others the past couple of days.  I see it every 10-15 seconds.  Even the sound sometimes gets garbled.  Other channels seem to be great.  This happens to the TVs using the contour box as well as the mini-boxes.  I have checked the ground connections outside (found it disconnected about a month ago) and they are good.  I have loosened and retightened the connections outside and inside.  There is one splitter inside (cable modem and tv) that has been swapped out.  I removed all the other splitters a few months ago when I put in a 8-port amplifier in place of the original 4-port amplifier (with splitters).  I'm not sure what else I can check myself.