jimbob79:charsleysa: To add to this, remember that your coaxial cable is most likely unshielded so it's susceptible to close range interference such as power cabling. If your power cabling and coaxial cabling happen to run near/beside/parallel to each other than feedback from the router being plugged in could be traversing your power cabling, crossing over to your coaxial cabling and interfering with your signal.
We had major renovations about 4 years ago and had new shielded coaxial cable installed. If it was a close range interference thing I would imagined it would effect all the digital channel and not just the +1 channels.
Did you try my recommendation? Even shielded cabling is susceptible to some degree, also it is possible to get interference through power cabling to the TV.