pixelated picture

I am having issues with pixelated channels, both HD and non-HD. Sound is fine and not affected. This only occurs during the day. Morning is fine and during the night it either goes away or becomes more bearable to watch shows.  Also, DVR shows are NOT affected. This is happening on both TVs that have a box, so it's not a TV issue or their respective boxes. I have disconnected and reconnected all cables. The system has been refreshed many times by myself and an Xfinity IT tech via chat to no avail. A coax line was installed and buried in my yard 10 years ago. The box outside my house is screwed shut with no obvious damage and definitely no way water can enter it or a rodent can get to the wires as the conduit is beyond thick; however, the other end of the line goes into a neighbor's yard, so I have no idea what that looks like. I've had nothing but horrible experiences with lazy techs coming to my house, that I'm hesitant to call until I know that, more than likely, the culprit is external. The "comcast test lab" via my remote says the signal is "good", so I believe the coaxial cables within my home are good. I don't see why those would be bad. I know corrosion happens, but those were also changed at 10 years.  If anyone has had a similar experience, please share before I lose my !@#$ mind.

Thanks.